The recent uncontained engine failure on the Qantas A380 in Singapore, as well as their recent similar mishap on a B747 at SFO, prompted the following question:
How many engine failures can an A380 (or other tri- or quad-jet) have, and still be able to maintain altitude? What about take-off? Once you’re past V1, how many engine failures can you have and still become airborne? I know that there is extraordinary redundancy in these modern airframes, but I’m curious just how far that redundancy goes.
Most of my familiarity is with twinjets, where the answers to these questions are much simpler: if one engine fails, you still have power, and can do stuff, if they both fail, you’re up a creek, and the best you can hope for is gliding to an airport in range, if you have a ram air turbine for hydraulics.
I’m also curious as to how the A380 compares to other quad-jets like the 747 and the A340, and to tri-jets like the DC/MD -10/-11, and the L-1011 in this respect.
Finally, in unpowered glider situations where the cause is something other than fuel exhaustion, (typically ingestion of hail/water/ash/birds into the engines), is starting up the APU a possible solution for more reliable hydraulic power than provided by the ram air turbine? Or does the APU require ground or engine power to start up? Do Tri- or Quad- jets even have APUs?
A NWA B744 experienced a bird strike leaving KSFO about 10 years ago, it dropped them down to 3 engines, which it made it back to SFO without a problem.
But as far as losing 2 or more, it depends on what has happened to cause those engines to be lost. Reference AAL191. They literally lost an engine, but because of the fuel transfer lines being severed when they lost the engine, they couldn’t stop the fuel leak. But depending how the engine loss occurred, and if it were contained, fuel would be routed to the remaining engine(s). Depends on how many engines you have left.
Another good point of reference is UAL292. When they lost their 3rd engine, the only thing that was the main cause of that incident was the loss of most vertical stabilizer use. The other 2 engines were fine. So it definitely depends on the situation the pilots are in to know how far you could go. Personally, if I dropped to 1 engine, I’d abort the takeoff if possible.
IIRC, a BA 747 had an engine failure on departure from LAX and continued on three engines. I think it had to divert into MAN though but made it most of the way to LHR with three. Most aircraft are designed to operate just fine with one engine failure.
In regards to takeoff, each type of jet should have a runway analysis associated with their performance, taking into account losing and engine(s) after V1 and in regards to the climb component.
