IFR minimums

Circling to Land
A circle at night is hazardous, combined with low visibility it is suicidal. Low level manoeuvring flight with few visual cues is as dangerous as flying can get. The circle to land is the second option to the straight in and if you have not briefed the circle you should execute the missed as a safer option. A straight in approach with high minimums or more than 30 degrees off the centre line is going to require a circle because you won't be able to get down to the runway on the straight in.

Your decision to circle requires that you fly the altitude and distance from the runway according to your airspeed aircraft category. Fly below 91 knots you are Category A; fly above 91 a bit and you're Category B. The distance difference is 2/10ths of a mile from 1.3 to 1.5. Maintaining the altitude during the circle is critical and the pilot must know the power and trim required to fly the bank angle at one altitude while keeping the runway in sight. Left turns are best if you need to keep the circle tight due to reduced visibility.

Once you lose sight of the runway you are expected to turn toward the airport, intercept the missed approach and fly the missed as published. If your circle lines you up on the runway get configured and slowed so as to get down in the runway landing zone.

Avoiding the Circle-to-Land
The design of the approach determines the requirements
Less than 400' per mile from FAF to threshold
Within 30 degrees of centreline
Course must cross extended centreline

Descent rate is from FAF to MDA at threshold may exceed 400 fpm.
Exceeds 30 degrees of centreline but not necessarily.
Course must cross extended centreline

You are expected to fly straight in and make descent if able. If unable, you must circle and keep runway in sight during your circle. Do not descend below circling altitude until established on final. Advise ATC of intentions.

On Circling to Land
Circling to land is a relatively dangerous manoeuvre. It contains the worst elements of IFR flight. There is a minimum obstruction clearance, a limited space in which to manoeuvre, an absence of visual reference, and trying to keep the runway in sight while preparing to land. At night it is a quite a bit more than dangerous. The required continuous turn in marginal conditions that keeps the airport in sight is hazardous. Many approaches that are aligned with the runway will have only circling minimums. You still may be able to land straight-in. Set up the missed approach procedure before beginning to circle. A circle to land requirement is a contact type of approach or otherwise a visual manoeuvre done with reference to instruments.

Because of the hazards associated with circling, flying the airplane must not be part of the problem. You must know the power settings and airspeeds that provide some safety margins. Trim the aircraft for the lightest possible touch. Let go when you look for the airport. Practice the flying about an isolated airport in good VFR to hone the MDA skills required in MVFR or LVFR conditions as for actual conditions.

During training you should make every circle to land approach with as close and short approach as you can handle without exceeding a 30-degree bank and your short field approach speed. This will give you a steep approach. If your circle puts you on a right downwind you might opt (tell ATC) to make a left downwind circle for better visual to the runway. Don't hesitate to take advantage of any wind to get down steeper and shorter. You are required to keep an identifiable part of the airport in distinct view except when concealed by a banked wing.

On an ILS approach you must have a localizer approach with a circle to land option. Most other approaches circle to land minimums published as well and straight-in. Circling minimums only are allowed for all approaches with a letter designation such as VOR-A. No straight-in minimums are published if the approach is more than 30 degrees; off the runway or a normal descent cannot made from MDA altitude. However, you are allowed to land straight in with the runway in sight and an ATC clearance. Request a 360 if you need to get down. In any circling approach keep the runway in sight and stay at MDA until clear of obstructions. If the VOR plate has a runway number it means that the approach is within 30-degrees of the runway and straight-in minimums will be published.

If you lose sight of the runway, overfly the airport, turn to your missed approach heading, and climb. The published missed approach is valid only when begun at the missed approach point at the MDA or higher. You are not promised terrain clearance if you do not follow the published procedure. No turns should be made until reaching the published missed approach point. Any other time you are on your own. The circling minimums presume a high degree of pilot proficiency and familiarity with the airport.

You have planned both the circling manoeuvre toward the airport and the missed procedure. You have pre-decided, because of the ATIS information, the approach angle sets which side to look for the airport. There are no required circling manoeuvres. With ATC clearance you are free to manoeuvre to a landing as long as the runway is in sight. Requirements of distance from airport centre (Category A 1.5 nm) and 300' clearance above obstacles are figured into the circling minimums.

Each category has a different minimum circling radii requirement that is stated in nautical miles for the aircraft category. Conversion of this to statute miles equals the visibility in statute miles as stated on the approach plate. The minimum obstacle clearance within each approach category circling manoeuvring area is 300 feet. Height Above Airport. (HAA) is 350 feet for Category A planes. VASI and PAPI equipped runways allow descent when within 10 degrees of interception. Publish minimums provide obstacle clearance only within the protected airspace.

ILS descent must not be below circling minimums for circling to be allowed. If there is a circling approach listed for the airport the circling altitude is the MDA. The MAP is based upon the FAF for the procedure as shown on the chart. An ILS approach for runway 27, circle to land runway 9 has its missed approach point at the designated missed approach point based on DME or on time and is a NON-PRECISION approach.

Every circle-to-land approach is a non-precision approach. The MDA of a circling approach gives an obstacle clearance of 300' but this is usually still lower than the normal pattern altitude. Check the charts to see if circling can only be in one direction. Only losing sight of the field due to banking is allowed. Any other failure to see the field requires that you start your climb to the missed-approach altitude, then turn in the direction of the protected obstacle-clearance region and fly the missed-approach heading. If you leave the MDA before intercepting the final approach course the FAA will blame you if you run into anything.

One way to fly circling minimums is to fly the glideslope down to the published circling minimums for the localizer and then proceed at MDA on the localizer by timing or DME if authorized. Another way is to fly the LOC to the straight-in minimums and landing straight in. If the published ILS approach is to be flown as a non-precision it makes sense to use the glide slope down to circling minimums. Basic rule is to fly the shortest path to base of downwind leg even if requiring you to overfly the airport. When appropriate all turns should be to the left.

Since a high descent rate usually has circling minimums only, you must be proficient in getting down quickly and in cleaning up during the missed. If you become visual with the runway by knowing where to look for the runway and are using a created VDP a straight-in is possible. Use no more than 30-degree banks in turns and do not rise above MDA by more than 50 feet. Only normal manoeuvres are allowed during descent from MDA. If at any point you lose visual contact with the airport and runway you must execute the missed. Don’t depart from the electronic glide slope until within one mile of the airport.

You could use a 90 left/270 right course reversal in a circle to land situation if conditions require. If possible, the turns should be made in the direction that gives the pilot in command the best view of the runway during the turns. Unless otherwise directed, the AIM procedure, if you lose sight of the runway, requires you to execute a climbing turn back to the landing runway and continue the turn to establish yourself on the published missed approach course. You are required to miss the circling approach when an identifiable part of the airport is not distinctly visible. If ceilings permit fly higher than MDA. A single pilot forced into right turns should not be circling.

The circling approach area is determined by approach category ("A" for C-172 for example). It is a series of arcs 1.3 miles in radius using all the runway ends and sides at the airport. Its size is the largest area possible made from these arcs. Category B is 1.5 miles. Primary obstacle clearance is only 300'. If obstacles are in the way no circling will be allowed. Obstacles of less than 400' may not be charted on the plates!!!! Circling in a specific direction may not be allowed. Study the chart. Occasionally it is necessary to remain at a higher than published altitude when transitioning to the approach. Occasionally, even the minimums vary according to the approach category. If the descent requires you to fly at a higher approach speed you must use the minimums for the higher category. Likewise, you must fly the missed approach published for the higher category. Obstacle clearance is assured only when using higher minimums for the speed flown. Higher minimums apply if an aircraft is flown at a higher category airspeed.

FAA figures a 400-fpm descent rate for the full approach but when circling is required the 400 fpm applies only to the MDA. A higher rate may be required below the MDA for the straight in approach. Don’t force it. Let the tower know if you do not plan to make a straight in. The PTS in Task E of the instrument approach procedures requires that an applicant know all the elements of the circle-to-land procedure. In a 22 word sentence the PTS says that the pilot must check the wind. At an uncontrolled airport this means to overfly the airport and check wind indicators. Basic procedure are to fly to the specified minimum, only if in visual conditions you circle to land on the designated runway into the wind. You are not allowed to descend below minimum altitude, go below visibility criteria or make other than a normal landing.

The circle is after ATC authorization when a straight-in landing is not the preferred option. Even if cleared for a straight-in you can circle only if you have not descended below the circling minimum. You have obstacle clearance if you remain within the radius of your approach category based only on your normal approach speed. The only way the examiner can participate in the flight is by maintaining a traffic watch. The missed approach instructions are based upon a straight in landing.

Since the circling approach will be coming in from nearly the opposite direction the direction of the missed turn will be reversed from the one published. The way you fly the circle is more apt to cause an accident than the weather. Circles are hazardous because you are low, slow, and turning. However, you are more likely to fly into the ground while on the centreline. Don’t circle if there is another option like landing downwind. Don’t circle with ice aboard. Don’t bust MDA. Use shallow banks. Never change from your decision to make the missed. A good missed is preferable to a bad circle. Regardless of the clearance, every missed approach begins with a straight-ahead climb with sufficient time to configure before initiating any turn.

63% fatal
51% stalls
31% icing

The Circle to Land
A circle to land in daylight is bad but circling to land at night is worse. Because two different procedures are involved. During the day the circle to land is actually a contact approach in which you must keep the runway in sight while remaining clear of clouds. At night the circle requires that you remain clear of clouds and below any ceiling. You do not have time to scan the instruments if you are watching the runway. It is best that you keep your speed up until lined up with the runway.

Once you lose the runway, turn to the runway and go for the published missed. If you haven't briefed the missed you are in considerable do-do. If you are not well prepared for the missed it is best to avoid making the circling approach. Go missed before you reach the airport by climbing to the MAP before making any turns. Do this because it does not require the flying skills, the planning and situational awareness that must be part of any circling approach or missed. Don't go near an icing situation during a circle to land.

Circling Not Allowed
A circling approach cannot be made if straight in descent has gone below circling minimums. Any circling must (should) be to keep the airport and runway to be used in sight from the pilot's side. There are no circling minimums for an ILS approach. Minimum descent altitudes may be published for straight-in-landings, circles-to-land or both. Don’t use a lower straight in minimum for a circle because the 250’ obstacle clearance only applies to the centreline of the approach. Because of obstacles the direction to circle may be restricted to higher minimums. Read the chart notes.

Missed Approach
While the preflight preparation included a complete run-through of the missed procedure, a review is done outside the FAF perhaps by noting the procedure written in crayon on the windshield. The prepared student asks questions about radio settings, identifiers, and any changes from ‘as planned’. Among the vitals of position awareness are your equipment settings.

You already have the missed checklist out. At the missed you must have pre-decided the sequence of events that you will perform. In addition to the sequence you have pre-decided the timing you will use. Talking is way down on the list. Get the power in, go to the heading, set pitch attitude, and remove some flaps. Gear later, talking later.

A mandatory reporting point. The IFR missed approach is more demanding that a VFR go around because it will occur in IFR conditions. The first consideration in low IFR conditions is to relate these to your personal minimums. If a missed approach is a possibility, it would be best to hand fly the approach instead of using autopilot. Controllers may be unfamiliar with where a Missed Approach procedure goes. The published missed approach is often a non-radar procedure and not very efficient. The missed approach course usually approximates the approach course. If you forget the missed procedure, add full power and climb on runway heading.

We often become slaves to our training and fly the total time to the missed approach. Rather, at our personal minimums and Visual descent point we would execute the missed. Get away from the ground and obstacles, climb on course and don't turn until the published time runs out. Don't clean up the plane until everything is under control. Since you have memorized the first part of the missed approach procedure and radios are pre-set you don't need to refer to the plate. Don't do anything in a turn during the climbing missed except control the turn.

Should you experience a full CDI deflection at any time you can climb but you MUST not turn before reaching the missed approach point. There is no guaranteed obstacle clearance protection beyond the full deflection of the CDI until we reach the missed approach point. An early turn may present obstacles that exceed your maximum climb rate.

You are likely to make the mistake of not applying full power only once. Power comes first, then pitch, positive rate, gear and flaps. Any change in the order is going to be exciting. Every missed starts with a climb. If you happen to have dual navs set them both to the approach. The other option, of using the second nav for intersections or missed or for distance means that re-setting is required. This distraction may (will) create problems. With flip-flop nav critical fixes become relatively easy.

The ILS missed approach point is a given when the glide slope meets the decision altitude. If you are inside the marker don’t try to salvage a poor intercept. Some say not to time for a localizer approach if it detracts from the ILS. Fly one approach at a time.

VDPs (Visual Descent Points) are not charted when DME is available or when there is no local weather advisory. The VDP gives a charted point from which to commence a normal landing approach with the runway in view. Use of the VDP is discretionary. While there are complex ways to use the DME to find the VDP for normal and possible landing slope to the runway the easiest way that will work consists of: Take 10% the MDH, subtract that number in seconds from the approach time. At that time, if you do not have the required runway visual indicators commence your missed approach climb and turn when the time runs out. This method flexes and works for both altitude and airspeed differences.

For the straight-in non-precision approaches nothing beats having a pre-planned visual descent point. There are several ways of getting a self-made VDP. The easiest way is to take the MDA (HAT or HAA) and drop the last digit. Use the remaining figures (2) as seconds to be subtracted from the approach time. The 3-degree descent rate usually desired can be obtained by multiplying your ground speed by five. At 100 knots a 500 fpm descent is close to a three-degree descent.

Missed approaches do not occur often but the missed approach should be a part of your proficiency training after you have the rating. Get to a safe altitude before you become upset with the weather forecast, ATC or yourself. The unexpected missed is the most difficult IFR procedure of all. It will be much harder if some instrument fails at this time.

The missed approach has several problem areas. Following an incorrect procedure can fly you into an obstacle at worst and at best may not return you to the correct fix. An approach flown too far due to failure to determine the actual ground speed creates a distraction problem. Looking for the airport is the most usual accident causing distraction. A mistake in your ground speed that makes you look for the airport after you have already passed it can be a fatal distraction. Use the ATIS wind direction and speed to predetermine the indicated airspeed you will use on the approach.

Preparation for the missed begins with the weather. An ATIS can be up to an hour old. Except for training purposes successful non-precision approaches in minimum conditions will create dangerous habits and presumptions. Save yourself the aggravation and proceed to a precision approach facility.

The stress level of a second approach after the missed approach is much greater than for the first. If the miss is because of procedure or technique, you could try again. If the miss is because of weather, find an alternate. The temptation to go below your personal minimums is greater on a second approach. The second approach has a disproportionate number of fatal accidents.

AN ATC warning of course or altitude DEVIATION is sufficient notice to begin THE MISSED. If you do not continue to fly the course procedure until the time has run out you will not have guaranteed terrain clearance. Do not turn until past the missed approach point. A climb is allowed but no turns.

More on Missed Approaches
Some characteristics of an emergency exist in the missed approach.

According to the FARs, you must have only three variables under control to avoid the missed.

First, you must be able to make a normal descent to a landing.
Second, you must have a visually identified runway, runway markings or lights
Third, you must have the minimum flight visibility required for the procedure.

Recognition of these requires judgment that is best acquired by experience. This experience requires that you plan in advance as to how you will perform to the specific conditions as they exist. For the non-precision approach you must come up with a visual-descent-point plan, know where to look for the visual runway clues, and know references for visual distance. For the precision approach there is no need for a visual-descent-point, it is best that at some point on the approach, say inside the inner marker, that you slow up and configure for landing. Runway behind you has no value.

While the DH of the ILS will allow a normal landing if you have slowed up, the MDA of the non-precision approach allows no such option. If you reach the MDA you will not be able to make a normal landing. You must accept the necessity for the circle-to-land procedure. You can decrease this necessity by getting to the MDA as soon as possible to increase your visual reference margin. Flying a slower approach speed is another way to avoid the circling approach. It helps to know the length of any lighting array and runway you are using. These should be a part of any pre-approach briefing.

Some minimum altitudes are published on charts. The published minimums are designed for the competent pilot. If you are less than proficient raise the minimums. Other minimums are only published for controller use. It is possible to request a lower than published altitude, if it exists it may be authorized. Such distinctions exist where flight along VOR to VOR routes have published altitudes but a vector airport to airport may allow a lower altitude via RNAV or radar vectors.

IFR airspace flows with the terrain. Minimum IFR altitudes in feet MSL are based upon obstacle clearance. Approaches are based upon descent angles, manoeuvring area, aircraft speeds, etc. FAR 91 operations have no landing minimums but according to aircraft and pilot capability the safety of FARs 121 and 135 should be followed.

You must plan any flight with knowledge of the underlying terrain. A vector may take you uncomfortably close to the terrain. ATC has been known to assign headings and altitudes that precipitate CFIT (controlled flight into terrain) accidents. As the ultimate responsible party you must keep aware of your terrain proximity and clearance.

Altitude Call-Outs

Stepdown altitudes
Where am I, cross-check?
No delay of missed
Second Pilot
1. Confirms briefing data
2. Calls altitudes
3. Calls missed
4. Calls runway

Altitude Minimums
ATC expects you to hold right on assigned altitudes as per FAR 91.123 regarding clearance deviation. In terminal areas ATC has a 200 foot margin before they get on your case. This allows for turbulence and altimeter errors. Centre and terminal rules have longitudinal, lateral and vertical minimums that vary somewhat if in radar or non-radar environment. Laterally in terminals it 3 nautical, in centres it 5 nautical with radar. Without radar it varies. Aircraft given vertical separation above 10,000 get merging traffic calls regardless but below 10,000 ATC is not required to give a call.

By asking for a visual climb, descent or separation the pilot has agreed to maintain VFR and visual separation. ATC likes this because it relieves them of responsibility.

FAR 91.129 Applies to aircraft on an ILS approach. It says that pilots are expected to remain at or above the glide slope as indicated by either the ILS or the VASI. No glide slope will intersect with an obstacle. Getting closer than the DA on an approach almost any fly-up indication could mean that there is an obstacle in your future. Maximum risk is inside the DH which is 200’ above the touchdown zone not the terrain below. Obstacle clearance may be as little as 120 feet. In a step-down approach you have a margin of 250’ obstacle clearance.

Your best way to handle obstacle clearance below MDA or DH is to use an existing or make a visual descent point, either by time or by DME. At three-degree glidepath intercepts these at a visual descent point. Most actual approaches do not reach minimums before breaking out. Slant range visibility is more important on an approach than vertical visibility.

Minimum crossing altitude MCA
Minimum descent altitude MDA
Minimum enroute altitude MEA
Minimum holding altitude MHA
Minimum obstruction clearance altitude MOCA
Minimum reception altitude MRA
Minimum safe altitude MSA

Maximum Elevation Minimums
Terrain figures for chart purposes are rounded off the nearest 100 feet and then 200 feet is added. The chart figures thus makes the elevation with a safety factor of from 201 to 299 feet. For obstacles made by man the figures are rounded up to the nearest 100 feet and then another 100 feet is added. The safety margin is then from 101 feet to 199 feet. The pilot is well advised to add some more.

Below Minimums Part 91 Operations
Under FAR Part 91 flight rules:

A 24 hour monitored ASOS at an airport will allow for alternate minimums
Any type of FAA approved weather forecast may be used to determine if minimums are met under FAR 912.169(c), including Area Forecasts.
Ceiling not a factor
Visibility as determined from the aircraft is key factor. This flight visibility can not be less than required by procedure
No descent below DH or MDA unless:

1) Position to make normal landing, and
Approach light system; threshold markings; runway end identifier lights; VASI; touchdown zone, its markings; or its lights or runway, its markings, or its lights are visible and identifiable, and
If 1) is missing a missed approach is initiated, or
If 2) not even one of the features is visible and identifiable a missed approach is initiated.

The FAA investigates all IFR landings made where below minimums visibility is reported. I suggest that you have difficulty hearing any ATC request for your flight visibility after an approach.

Standard Minimums

For a precision approach (glide slope) 600' ceiling and 2 miles
Obstacle clearance for precision approach is 121’ trapezoidal area tapering to runway.
Obstacle clearance on intermediate segment (procedure turn) is 500’
Obstacle clearance on feeder and transition routes is 1000’ + depending on terrain.
For a non-precision approach 800' and 2 mile visibility
Obstacle clearance is minimum of 250’ trapezoidal area with no greater clearance in any one area over another.

Procedures with a FAF all have 250’; a VOR without FAF is 300’; NDB with FAF is 300’ and without is 350’.

Obstacle clearance on intermediate segment (procedure turn) is 500’.
Obstacle clearance on feeder and transition routs is 1000’ + depending on terrain.
FAR 91.l15 allows descent below DH or MDA to TDZE+100 with any part of the approach light system in sight. To descend below TDZE+100 requires having the terminating bars, siderow bars etc. in sight.

ATC separation minimums are 1000 vertical and three miles laterally and 2000' and five miles above 29,000.
Visual separation by the pilot applies only if an approves form of separation is confirmed. The purpose of
making the pilot responsible is to reduce radio congestion and reduce burden on controllers. Once a pilot
acknowledges visual contact the responsibility for separation is his until he says he no longer has visual contact.

Personal IFR Minimums
Every pilot who has flown into unexpectedly low IFR conditions has come away with an appreciation that it is necessary for him to set personal limits for his IFR flying. Every IFR flight has to be weighted with the pilot's evaluation of his skill and experience, familiarity with the aircraft and instrumentation, local awareness of terrain and obstacles, and the 'need' to fly.

A second pilot in front with you is always a good idea. The unexpected on takeoff that prevents a return due to below minimums weather, requires an immediate flight to the nearest safe haven. The setting up of departure and arrival procedures can always use another pair of hands and a mind as back up. Single pilot IFR is very lonely. Any departure from a field that cannot be returned to is certainly challenging the Gods.

Parts 91.167 and 91.169 spell out the minimums that must exist one hour before until one hour after your ETA at original destination must have 2000' ceiling and three mile visibility. Should conditions be lower you must have an alternate airport with precision approach limits of 600' and two-mile visibility or a non-precision approach with 800' and two miles. IFR Fuel requirements apply. The safety of a specific flight at any specific point of this flight is directly related to the selection of options you have available.

Takeoff Minimums
Set radios for the IAP for the other end of the runway. An even better might be a GPS or VOR approach to a crossing runway. Part 91 can depart but other Parts cannot depart if conditions will not allow a return to departure airport. If conditions are below landing minimums but above takeoff minimums we must have an alternate airport that is within one-hour flight time. Taking off in zero-zero Part 91 is legal but you must know where you will go if something stops working. Takeoff minimums are not mandatory on FAR 91 operations but the Part 91 pilot should be aware of the FAR 121,129 and 135 minimums. A chart may show takeoff minimums and still not have an IFR departure (Not Part 91)

Zero-Zero Takeoff
There are no accident figures that preclude zero-zero takeoffs as being dangerous. The acceleration of the aircraft can cause a somatogravic illusion that you are more nose up than it seems. Pilots who habitually make zero-zero Part 91 departures tend to be confident of their abilities and the maintenance of their aircraft.

The risk in a low-visibility takeoff lies in loss of control. Control can be lost during ground acceleration or in the transition from seeing the ground and entering MIC. You do not have any prep-period for the instantaneous change. Acceleration is a vertigo producer and the pilot must know that illusions will occur and gauges must be believed.

The next immediate risk is loss of power. Even if you know the area, low-visibility blinds you and trusting to blind luck is not a good choice. It is for these reasons that the airline minimums of one mile visibility are good minimums for the Part 91 pilot, too.

Low visibility takeoffs and departures have as an inherent factor flight close to the ground and unseen obstacles. The hazard of the takeoff is the abrupt transition to a full IFR workload. Part 91 has no minimums for takeoff but as with any other IFR takeoff it has four phases:

This is where you taxi into position, align with the centreline, check and set compass to HI, hold brakes while you use power to give you rudder control before brake release, and go to takeoff power.

(2) Roll;
You use rudder rather than brakes to control rolling heading. If you can set a localizer frequency the CDI has a one dot range of 70 feet to each side. Keep the CDI centred. Acceleration can fool the AI into a nose-high indication so be smooth.

Rotation speed should be slightly faster than usual and relatively positive and smooth. Let the plane fly off and get on the gauges. Apply right rudder. Get at least 100' before changing gear or flaps. Waiting longer is usually better.

(4) Initial climb.
Maintain two bars on the AI and confirm airspeed and VSI both of which may lag due to static error.

Climb Minimums
FAA climbs and climbs to minimum altitudes are predicated on crossing the departure threshold at 35'. You are required to report to ATC anytime you are unable to climb 500 feet per minute.

Non-Standard Minimums
An airport that meets the weather forecast may not be legal if it has non-standard minimums. (Jepp on airport diagram sheet). A NOS chart may show an A for an airport where Jepp charts may not because Jepp does not chart for Category E aircraft.

Sidestep Minimums
Sidestep landings to parallel runways have higher minimums than straight in approaches. Sidestep should be done as soon as runway is in sight.

Obstacle Clearance Minimums
Obstacle free zone (OFZ)
May be used in specific region near airport. From end of runway away from MAP you have 1/2 nautical mile obstacle clearance area. This area extends in an ever widening angle to 13.5 NM. At 13.5 NM the primary safe area extends 4 nm to each side of centre line and the secondary safety area is an additional 2 nm to each side. MOCAs insure obstacle clearance by 2000' lateral and 1000' vertical and navigational signal within 22 nautical of Navaid. In some instances as over the hills of Vallejo and Hayward the proximity of the terrain is much closer.

Every airport with an instrument approach procedure also have a departure procedure if obstructions are present in the terminal area.
An IFR departure is available for safety when terminal area obstructions cannot be seen or avoided.
Obstacle clearance is assured if the departure end of the runway is crossed above 35’ and climbs to 400’ before turning.
At this point a climb of 200 fpm will clear obstacles up to the enroute airways.
This and any published rate of climb will clear obstacles by 35’.
NOS charts have a T to advise of non-standard requirements.
90 knots per nautical mile gives a climb rate per minute of 300 where only 200 fpm may be required.
If 350 fpm is required you should climb at 525 fpm.
If terrain is above runway elevation the obstacle clearance may be a little as 120’ even though the DH is at 200’.
The further away from the runway the greater the obstacle clearance.
Laterally the protected airspace is 1000’ wide when 200’ from the threshold.
At ten miles the lateral dimension is five miles to each side of the centreline with the outside mile tapered upward.
Your obstacle clearance may be as little as 70 feet.

VOR/DME with FAF, Straight-in 250 250
VOR/DME, radial or arc final 500 500
NDB on airport, no FAF, straight-in 350 350
NDB obstacle clearances become wider toward the runway. This accounts for the higher minimum descent altitudes
NDB w/FAF, straight in 300 300
Localizer, LDA, SDF 250 250
GPS approaches usually become narrower toward the runway. Therefore, the MDAs are lower. Cannot be used to track courses unless there is an overlay. It is o.k. to fly the missed or a transition but not the approach.

Circling 300 Tapers to 0

Holding 1,000 500DF Approach 500

In the secondary area the obstacle clearance tapers to zero at the outer edge. The greatest clearance is on the centreline.

Approaches with 500’ minimums will have higher obstacles. Check the circling area.

If you intend to land, you must at some point descend below the MDA and DH. The closer you get to the runway the less your obstacle clearance becomes. The non-precision minimum is 250’. The visibility minimums of all approaches are determined by the slope to the runway. It is possible to have an obstacle intrude into the glide path inside the DH if visibility minimums are over one mile.

Minimum Vector Altitudes
Controllers are required to issue an altitude to maintain that provides obstacle clearance until on a published segment of the approach. MVAs are used by radar controllers depending on radar quality and the distance from the antenna. Controllers often put in their personal fudge factor to protect themselves.

Minimum En route Altitude (MEA)
The MEA provides at least 2000' of clearance above enroute obstacles when the route is over mountainous terrain and 1000' otherwise.

An MEA assures reception of VOR signals. VHF communications are usually but not always possible.
MEA guarantees radio communication on airways. Communication is guaranteed at FAF and at missed approach point.
There is no assurance of communications anywhere else during the approach.
Don’t accept as gospel the MEA altitude during very cold conditions.
Request or fly at least a thousand above MEA.

Minimum IFR Altitude
The MIA is on unpublished direct ATC routes established by the facility. Any ATC clearance will give restriction to keep pilot above MIA.

Minimum Safe Altitude
If there is no nav facility within 30 nm of the airport, there will be no MSA. MSA provides 1000' clearance above the highest obstacle in a defined sector. Be sure to check plates to see facility used to determine MSA distances.

Minimums Off Airways Altitude (Jepp MORA /FAA OROCA
IFR pilots operating on an IFR flight plan off a designated airway must ensure they operate at a safe altitude based upon the requirement of FAR 91.177. Actual flight information can only be determined by use of sectional plus any NOTAMed new obstacles.

The pilot is responsible when operating off-airways on a direct routing for determining the minimum en route altitude. In mountainous terrain the minimum IFR altitude for off-airway operations is 2000' above the highest obstruction within 4 miles either side of your course.

Minimum off route altitude. On Jepp shown at 6000' or lower gives obstacle clearance of 1,000'. Above 7000' there is 2000' clearance. This is only obstacle clearance no reception or navigation included.  The acronym MORA stands for minimum off-route altitude. It's a Jeppesen term, found only on Jeppesen charts and defined in the company's chart glossary as "An altitude derived by Jeppesen...it provides known obstruction clearance within 10 nm of the route centreline."

NOS Off-Route Obstruction Clearance Altitude (OROCA) and Jepp's Minimum Off-Route altitude (MORA) are supposed to provide obstruction free direct routes. These altitudes are the same as appear in each quadrant of the sectional charts.

Minimum Descent Altitude (MDA)
As written by the FAA the lowest altitude, expressed in feet above mean sea level, to which descent is authorized on final approach or during circle-to-land manoeuvring, in execution of a standard instrument approach procedure where no electronic glideslope is provided.
Lowest mean sea level altitude during non-precision approaches.

This is one of the most dangerous flight altitudes in all aviation. Single pilot operations that require the pilot to find the runway indicators make the presence of an flight ‘looking’ assistant very desirable.

Descent Minimums
You cannot deviate from the published approach procedure unless you are in VFR conditions and you have cancelled IFR with ATC. The published IFR altitude for a final approach segment is the minimum descent altitude. (MDA)

Requirements for descent below Minimum Descent Altitudes. (MDA)

1. Aircraft in position to make normal approach and landing
2. Approach threshold or approach lights or other airport markings are visible to pilot.
3. Flight visibility is not less than prescribed visibility for the approach.
4. Arrival at missed approach point or thereafter requires both 1, 2, and 3 above or a missed approach must be
commenced. FAR 91.175
5. Doing the published approach may give lower (ice free) altitudes than taking vectors due to vector minimums.

#1 of the above creates a particular problem for non-precision approaches where the runways are typically shorter than for precision approaches. Any excess airspeed carried in the approach but not required for landing must be dissipated. Diving for the runway will not work. The placement of the non-precision missed approach point precludes a normal landing unless the landing decision can be made prior to reaching the missed approach point.

It is usually considered better to be at the MDA well before you reach the missed approach point since it allows you to design a VDP from which you will be able to perform a normal landing. An additional advantage is the stabilized level arrival allows more time for creating the best landing configuration ahead of time with sufficient time to configure for the missed approach. If you can't make a normal landing you will be below the circling minimums, you must execute the missed.

Having the missed approach point at the end of the runway will preclude the making of a normal landing approach unless the runway is over a mile long. or if a strong headwind exists. Time and airspeed must be under control or serious problems of decision making will arise.

Circling Minimums:
1. Do not descend or use flaps until on final
2. Any airspeed greater than 91 kts raises your category.
3. Lose sight of runway--GO AROUND by flying runway heading in a climb. You must have an identifiable
portion of the airport in view visible to the pilot while above the MDA.
4. Only circling minimums are published in a letter coded approach (VOR-A) straight-in minimums are not
authorized but if conditions allow you may land straight-in.
5. You do not need to worry about other aircraft inside the circling manoeuvring area when in Class D airspace.
6. You may well be concerned about other aircraft when flying circling minimums at an uncontrolled airport. Left
patterns unless contra indicated.
7. Circling at night is more dangerous than during the day.
8. Do not descend below MDA until on base leg. If at an unfamiliar airport fly the MDA of the class D aircraft for greater flexibility and obstacle avoidance.

Non-ILS Circling Minimums
One way to fly glide slope down to localizer circling minimums. Then proceed at MDA on the localizer by timing or DME if authorized. Another way is to fly the LOC to the VDP and landing straight in or fly the ILS to the circling minimums for the circle.

Straight-In Minimums
A straight-in approach has minimums of alignment and descent. A descent gradient of 300' per mile from the FAF to threshold is standard but 400' can be used. The approach course must be within 30 degrees. Some straight-in approaches have only circling minimums because of obstacles. If visibility allows you see the runway requirements at the circling minimums you can land straight-in. You should have a VDP pre-decided in such an event. A straight in approach mandates than a procedure turn may not be performed unless a specific clearance is obtained.

Non-precision criteria for minimums can have obstacles above the MDA within one mile of the approach fix. Chop it and drop it procedures are not ALWAYS the best way to fly. A straight in may have only circling published minimums if the approach will not allow a normal descent. If you maintain the circling MDA and can make a straight in without excessive manoeuvring or rate of descent, get the clearance and do it.

Estimated Time of Arrival Minimums
If you find your ETA to a fix is going to be off by over THREE minutes you should advise ATC. The safest ETA estimates seems to be "6" minutes.

Alternate Airport Minimums
FAR 91.103 says that pre-flight includes knowing runway length, aircraft performance and alternatives available if the planned flight cannot be completed. FAR 91.167 adds fuel required to destination, then to alternate and then for 45 minutes. Based on these FARs, especially FAR 91.169, an alternate (plan) is required for all IFR flights except when destination has an approach and is forecast to be 2000' and three.

An approved alternate must have weather reporting (It can be an area forecast) and the instrument procedure must be continuously monitored. If an airport is not authorized as an alternate one of these factors is probably missing. Where a planned alternate has more than one approach, one of them may be listed as NA as an alternate. The airport can be used only if another approach is used.

Required if not:
Standard 600'& 2 precision; 800' & 2 non-precision. Requires operating weather observer on site or AWOS/ASOS
Mnemonic: ABCD123 = 1 hour After/Before, Ceilings 2000', Distance 3 miles.

Published in DPs, STARs, Terms and Tables.

On an IFR flight plan into an airport without an instrument approach, you MUST have an alternate regardless of weather.

The prudent pilot sets his sights on the "filed paper' alternate early on. If the ceiling is forecast at the destination to be less than 2,000' AGL and visibility less than 3 miles, an alternate is required. A terminal forecast (not Area) is required for determining alternate weather minimums. "Occasional implies 50% chance or greater and "chance" is less than 50%.

Terminal weather observation and reporting facilities must be available for the airport to serve as an filed paper alternate airport. If the weather is good as, required in FAR 91.169 to descend from MEA and land in basic VFR, all you need for planning is an area forecast saying so and a runway. Even when an alternate is not required you must have options in mind.

ATC has no record of your filed alternate option. As a Part 91 pilot you should have immediately at hand a takeoff alternate with plates available. The idea is that if you can't return to your departure field you should have a near-by airport available as an real emergency as required alternate.

Minimum Sector Altitudes
MSA give 1000' obstruction clearance within 25 NM including mountains. MSA is measured from markers on ILS approaches, the NDB on NDB approaches and runway threshold on GPSs. MSA does not apply in mountains, which require 2000' obstacle clearance.

The Minimum Safe Altitude
The Minimum Safe Altitude (MSA) circle has nothing to do with the approach or the initial approach altitude or the approach segments or the procedure. The MSA is for emergency purposes only. Minimum vector altitudes (MVA)are usually below the MSA. The required obstacle clearance (ROC)of the TERPS procedures for making an instrument approach procedure also set that the ROC of the MSA must be 1000’ higher than any obstacle within the circle. The MSA circle may be divided into sectors for any approach except for the GPS approaches. The MSA is essentially a non-functional part of the approach plate.

Rule of Thumb:
Take half of your ground speed and add a zero. Read result as fpm descent rate for a 3-degree slope. As with so many things about flying, getting away with a descent below minimums may be the worst thing that can happen to you. Just because something like this works at airport A is NO reason to believe it will work at B. Obeying minimums is a guarantee that you will live to fly another approach.

Normal Landing After MDA
If you shoot a non-precision approach at MDA and time, it is unlikely that you will be able to make a normal landing. The nose will block your view of the runway at the missed approach point. Your legal options are to apply flaps early to improve your ability to see the runway. The more flaps you use the better you will be able to see the runway and the lower will be your stall speed.

FAA Separation Requirements

The most tightly limited requirement relates to assigned altitude.
When in other than Classes B or C airspace, ATC is not charged with separation of IFR from VFR traffic.
In Class E, ATC may call out traffic but there are no separation requirements.
Over 10,000 feet ATC will advise of traffic than is merging. POTUS gets merging advisory all the time.
You have only one minute to ask for a vector to avoid traffic before you will be meeting that traffic.
Course deviations are not as likely to cause a problem as are altitude deviations.
You can declare an emergency and then deviate. You may be asked to give an explanation.
Everything ATC says and that you say is tape-recorded.
Keep an ASRS NASA form in your flight bag and fill it out just in case.
Anything you say on the radio can be used against you.

Minimum En route Altitudes

Provides altitude buffer above controlled airspace of 500' and 300' for transition areas with exceptions.
Guarantees communications if not with ARTCC then another ATC facility.
Will be above the MOCA, which provides 1000' as standard and 2000' in mountains.
Be at or above the MRA
Allow crossing VOR radial without DME
Exception is where MRA is higher and noted on chart.
Adequate for crossing a fix with higher MEA on other side.
Where MCA is established for a fix it is because the minimum climb rate required exceeds standard.
Provide an acceptable navigational signal for route.
Where gaps occur, they are noted on the charts.

Minimum Descent Altitude (MDA)
— The lowest altitude, expressed in feet above mean sea level, to which descent is authorized on final approach, or during circle-to-land manoeuvring in execution of a standard instrument approach procedure where no electronic glide slope is provided.

Minimum En route Altitude (MEA)
— The lowest published altitude between radio fixes that guarantees adequate navigation signal reception and obstruction clearance (2,000 feet in mountainous areas and 1,000 feet elsewhere). It is normally the lowest altitude you would use during an IFR flight on airways.

Minimum Sector Altitude (MSA) — The lowest altitude which may be used under emergency conditions which will provide a minimum clearance of 300 m (1,000 feet) above all obstacles, located in an area contained within a sector of a circle of 46 km (25 nautical mile) radius centred on a radio aid to navigation.