FAA Instrument Rating Airplane (IRA)IFR Procedures and ChartsMedium
A pilot is flying direct via GPS on an off-airway route over mountainous terrain with no MEA, MOCA, or other minimum altitude established for the route. The highest obstacle within 4 nautical miles of the course is 8,150 feet MSL. Per 14 CFR 91.177, what is the minimum IFR altitude the pilot may fly?
- A9,150 feet MSL
- B8,150 feet MSL
- C10,200 feet MSL
- D10,150 feet MSL
Show answer & explanationAnswer & explanation
Correct answer: C. 10,200 feet MSL
14 CFR 91.177 requires, in mountainous terrain with no charted minimum altitude, at least 2,000 feet above the highest obstacle within 4 nautical miles of course, rounded up to the nearest 100 feet. 8,150 + 2,000 = 10,150, which rounds up to 10,200 feet MSL.
Why the other options are wrong
- A. Incorrect — this uses the 1,000-foot non-mountainous clearance value, not the required 2,000 feet.
- B. Incorrect — this is just the obstacle height with no clearance margin added.
- D. Incorrect — this is the unrounded sum; the regulation requires rounding up to the nearest 100 feet.
91.177 Minimum IFR Altitudes (Off-Route)
When no MEA/MOCA/MCA is established, IFR flight must be at least 1,000 feet (non-mountainous) or 2,000 feet (mountainous) above the highest obstacle within 4 NM of course, rounded up to the nearest 100 feet.
- Mountainous areas require 2,000 ft clearance
- Non-mountainous areas require 1,000 ft clearance
- Always round up to the next 100-foot increment
Memory trick: Mountains need 2,000 — flatlands need 1,000, always round UP