Minimums
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, maneuvering 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 alltitudes
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. Center 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 centers 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.
At some point, in every young persons education, it is usual to explain the facts of life. Such is also typical of IFR instruction. At some point an instructor must reveal to the trainee that the bending of an occasional FAR minimum varies from questionable to suicidal. Most such violations are deliberate. 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
2) 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)
Continue To Next Page