Category: How flying works
Why One Failure Rarely Brings an Airliner Down
Short answer
Airliners are designed on the assumption that any single part can fail on any flight. US certification rules say a single failure must never lead to a catastrophe, so important systems come in two or more independent copies, failures are shown to the crew, and there is a written procedure for each one. That is why a failure usually ends with the crew choosing to land sooner, not with an accident.
What was reported in October 2026
On 23 October 2026, the US Federal Aviation Administration (FAA) said, a business jet returned safely to the airport it had left after the crew reported a hydraulic issue. On 26 October a regional jet arriving from Mexico landed safely after the crew reported a possible braking and steering issue. The FAA said it will investigate both; neither statement gave a cause.
This page does not explain what happened on those flights. It explains the design idea behind both safe endings.
Fail-safe: assume it will break
The FAA's advisory circular on system design (AC 25.1309-1B, 2024) tells the makers of large aeroplanes to assume that any single element, component or connection can fail during any one flight, however unlikely that is, and says such a single failure must not be catastrophic. Further failures on the same flight must be considered too.
The rule behind it, 14 CFR 25.1309, says every failure condition that would be catastrophic must be extremely improbable and must not result from a single failure. The circular puts "extremely improbable" at the order of 1 in a billion per flight hour, or less.
Backups, separation and warnings
The circular lists the techniques designers combine, noting that one alone is seldom enough. Redundancy keeps a function working after a failure; its own examples are two or more engines and two or more hydraulic systems. Isolation keeps the failure of one system from taking down another. Failure indications tell the crew something has gone wrong, and flight-crew procedures say what to do about it.
Landing gear is a clear example. US rules require an emergency means of lowering it if the normal system fails or if any single source of hydraulic or electrical power is lost. Our page on landing gear problems explains how that works.
What the crew does
Warnings and procedures are part of the design, not an afterthought. When a warning appears, the crew works through the checklist for it, and very often decides to land sooner than planned: back at the departure airport, or at another one on the way. That can give them a long runway, engineers and emergency services on the ground. A safe return, like the ones in the FAA statements, is the backup and the procedure doing their job.
In AeroFox
AeroFox's trainers have a single engine, so for them there is no second engine to take over. Even then a failure has a trained answer. In the engine failure lesson you fly the best-glide speed and land on the runway without power; in the engine failure after take-off lesson you reject a take-off on the runway and, if the engine stops just after take-off, land straight ahead.
If you are a passenger
A turn back, a diversion or fire engines beside the runway can be unsettling. They are what a cautious crew and a well-designed aircraft look like when something has failed. Keep your seat belt fastened, listen to the crew's announcements and follow their instructions.
Common mistakes and myths
- A warning on the flight deck does not mean the aircraft is about to crash: designers assume parts will fail and build around that.
- A return to the departure airport is not a sign that the crew panicked; it is often the most cautious choice.
- Backups do not make a failure unimportant: crews take each one seriously and land so that it can be checked.
- Fire engines waiting by the runway do not mean a fire is expected; they stand by in case.
Questions people ask
Can an airliner keep flying if one hydraulic system fails?
Airliners are designed for that: the FAA circular gives two or more hydraulic systems as an example of redundancy. The crew follows the procedure for the failure and decides where to land.
What does "extremely improbable" mean?
In the FAA circular, on the order of 1 in a billion per flight hour or less. Catastrophic failure conditions must be that unlikely and must not come from a single failure.
Why go back instead of carrying on?
The FAA statements do not give the crews' reasons. In general, landing sooner, at a known airport with engineers and emergency services, gives the crew time and help to deal with a fault.
Practise it in the simulator
Fly the trainer's engine failure lesson: the engine stops 1,800 ft above the runway, and you fly the best-glide speed and land without power. The engine failure after take-off lesson teaches the other half: reject a take-off on the runway, and land straight ahead if the engine fails just after take-off.
Start this lesson: Engine failure
Another lesson on this topic: Engine failure after take-off
Related explainers
Sources
- Statements on aviation accidents and incidents: entries of 23 and 26 October 2026 (FAA)
- Advisory Circular 25.1309-1B: System Design and Analysis (2024) (FAA)
- 14 CFR 25.1309: Equipment, systems, and installations (Legal Information Institute, Cornell Law School)
- 14 CFR 25.729: Retracting mechanism (emergency extension of the landing gear) (Legal Information Institute, Cornell Law School)
About these explainers
AeroFox is a free, public-interest project with no paid features. The explainers are written by the AeroFox team from public sources such as FAA handbooks, NASA and regulators, and, for the lessons from the news, from the news reports we link to. Each page lists its sources, and pages are updated when the facts or the lessons change. They explain ideas. They are not flight instruction, medical advice or legal advice, and they do not count toward any licence.