Backup Systems: A Spare for Everything That Matters
2 min read
The short answer
Airliners are designed so that no single fault can put the flight at risk. Engines, hydraulics, electrics, computers and navigation all have backups — often with backups of their own. A twin-engine jet can even take off, fly and land on one engine.
Designed So No Single Fault Matters
Planes are designed around one simple rule: no single fault should put the flight at risk. This is called redundancy. Almost every important system has a backup — and often a backup for the backup.
Engines
Every twin-engine airliner can take off, climb, cruise and land on one engine. It must prove this before it's allowed to carry passengers.
Engines are also extremely reliable. Before planes can fly long routes far from airports (called ETOPS), regulators require proof of very low engine shutdown rates.
Hydraulics
Hydraulics move the wing and tail surfaces and the landing gear. Airliners have two or three separate hydraulic systems. If one stops working, the others keep the plane fully controllable.
Electrics
Planes have several generators — usually one on each engine, plus one in the tail — and batteries too. There's even a small wind turbine that can pop out under the plane to make power if everything else were lost.
Computers and Navigation
Airliners have several flight computers that constantly check each other. If one disagrees, it's outvoted, and the pilots can always fly by hand.
Navigation works the same way. GPS, onboard motion sensors and ground radio beacons all tell the pilots where they are. If one stops working, the others carry on.
Communication
Pilots have several radios, and many planes also have satellite links. They can stay in touch with air traffic control even over remote areas.
The Thinking Behind It
Engineers assume that, in any complex machine, something will eventually go wrong. So every system is designed so that a fault is:
- Spotted straight away
- Handled safely
- Never critical to finishing the flight
What This Means for You
Your seat sits inside layers of backups, tested and refined over decades. The plane you're on didn't pass one safety test. It passed thousands.
Sources
- FAA, 14 CFR 25.1309 — Equipment, systems, and installations (the "no single failure" design standard): https://www.ecfr.gov/current/title-14/section-25.1309
- FAA, 14 CFR 121.161 — Airplane limitations: type of route (ETOPS): https://www.ecfr.gov/current/title-14/section-121.161
- FAA, 14 CFR Part 25 — Airworthiness standards: transport category airplanes: https://www.ecfr.gov/current/title-14/part-25