Large transport category airplanes: Turbine engine powered: En route limitations: Two engines inoperative

This regulation sets en route performance requirements for Part 135 operators flying turbine-powered large transport aircraft with more than two engines, assuming two engines fail simultaneously. The specific requirements depend on the airplane's certification date.

All three certification categories offer two compliance options:

1. 90-minute rule: Stay within 90 minutes (at normal cruise) of a suitable airport at all times, or

2. Performance-based: Operate at a weight that allows the airplane to reach a suitable airport after losing two engines, maintaining required terrain clearance using the net flight path data from the Airplane Flight Manual.

The terrain clearance requirements vary by certification date—older aircraft (pre-1958) need 1,000 feet above terrain or 5,000 feet MSL, whichever is higher. The newest category (post-1959) requires 2,000 feet clearance and includes additional fuel reserve requirements (enough to reach the airport at 1,500 feet above it, plus 15 minutes cruise fuel).

This ensures multi-engine aircraft can safely reach an airport even after losing two engines.

*This is a plain-English summary for study only. The official 14 CFR text on this page is controlling — always read the current regulation and consult a CFI.*