Can Planes Fly With One Engine?
Sources: FAA Part 25, ICAO Annex 6 · Updated May 2026
Yes — every twin-engine commercial airliner is certified to fly safely on a single engine. FAA Part 25 (and EASA CS-25) require that a transport-category twin can take off, climb, cruise, divert, and land with one engine completely inoperative. ETOPS (Extended Operations) rules go further: a twin operating long-haul ocean routes must remain within a specified single-engine flying time of a suitable diversion airport — commonly 180 minutes, with some approvals out to 370 minutes. ETOPS certification has been mandatory for transoceanic twin operations since 1985 and was extended to 180 minutes for the US fleet in 1989; the modern Boeing 777, 787, Airbus A330, A350 fleets all operate routinely with ETOPS-180 or higher. The fact that you have flown across the Atlantic or Pacific on a twin-jet is direct operational proof: every flight assumes single-engine viability.
The certification baseline
FAA 14 CFR Part 25 — the airworthiness standard for transport-category aircraft — specifies minimum performance with one engine inoperative (OEI) at every phase of flight:
- →Takeoff (Part 25.111, 25.121): after V1 the aircraft must continue and clear obstacles with the failed engine. Climb gradients of 2.4% (twin, second segment, gear up) are required.
- →En-route (Part 25.123): the aircraft must be able to maintain a defined climb gradient at its OEI ceiling, with terrain clearance over the planned route.
- →Landing (Part 25.119, 25.121): certified single-engine go-around capability at landing weight.
The same standards exist in EASA CS-25 with minor differences. They are not optional: an aircraft cannot be type-certified without demonstrating all of them in flight test.
ETOPS — flying long over water on a twin
Before ETOPS, transoceanic flying was the exclusive domain of three- and four-engine aircraft (DC-10, L-1011, 747). The ETOPS rule (introduced by the FAA in 1985) allows two-engine airliners to fly long routes provided that the aircraft, engine, operator, and route together meet stringent reliability and operational standards.
To earn ETOPS certification the engine must demonstrate an in-flight shutdown (IFSD) rate at or below 0.02 per 1,000 engine-hours for up to ETOPS-180, and 0.01 per 1,000 engine-hours for approvals beyond 180 minutes. Operators must maintain crew training, dispatch reliability, and maintenance procedures specific to ETOPS.
Performance with one engine inoperative
From a typical cruise altitude of FL370, a twin with one engine out cannot maintain that altitude at full weight. It drifts down to its one-engine-inoperative ceiling — typically FL180–FL250 for narrow-bodies, FL200–FL270 for wide-bodies. The aircraft remains controllable and well above any terrain. See what happens when an engine fails.
Single-engine cruise speed is roughly 0.70–0.78 Mach, slower than the normal 0.78–0.85 Mach cruise. The aircraft has full range to reach a diversion airport.
Single-engine approach is a standard simulator exercise; line pilots practice it every recurrent training cycle. Asymmetric thrust requires rudder input, but autopilot remains available for most of the approach.
Has it actually happened?
Yes — many times, in routine, uneventful fashion. A few well-documented examples:
- →United 232 (1989): A DC-10 lost all hydraulics after the centre engine disintegrated. Crew used differential thrust on the two remaining engines to control the aircraft. 184 of 296 survived. While a three-engine case, it illustrates how engineered redundancy and crew skill combine in extreme cases.
- →Air Transat 236 (2001): Airbus A330 lost both engines mid-Atlantic due to a fuel leak — and glided 75 nautical miles to a safe landing in the Azores. Zero fatalities.
- →Routine ETOPS diversions: dozens occur each year worldwide. Most are precautionary (oil pressure warning, fuel filter caution, vibration indication) and end with a safe single-engine landing at the planned alternate.
What about three- and four-engine aircraft?
The same logic applies. A Boeing 747 or Airbus A380 can fly on three of its four engines with little performance loss; the certification baseline is "one-engine-out" or more in some cases. The widebody trend over the past three decades has been toward twins (777, 787, A330, A350) because ETOPS reliability targets have made them as proven as quad-jets for long-haul service, while burning much less fuel.
Sources
- FAA 14 CFR Part 25 — Airworthiness Standards: Transport Category Airplanes
- FAA 14 CFR Part 25 Appendix K — Extended Operations (ETOPS)
- FAA Advisory Circular 120-42B — Extended Operations
- ICAO Annex 6 Part I — Operation of Aircraft
- ICAO Doc 10085 — Manual on Extended Diversion Time Operations
- EASA CS-25 — Certification Specifications for Large Aeroplanes