Posts about: "RAT (All)" [Posts: 607 Pages: 31]

I believe that particular bug is fixed, though it's always possible there's other issues causing a total AC loss.

Not really relevant to what you quoted though, as the scenario in question requires:

• Engines running on centre tank fuel during takeoff while the aircraft is operating normally
  • We don't know for certain if this is the case. It seems to be but it's not something that happens on other families.
• Then, total AC failure stopping fuel boost pumps.
• Engines suction feed from contaminated/full-of-water wing tanks.

The aircraft has two engines and should be able to climb out on one, plus it dropped like a rock . 'Significantly degraded' thrust isn't really compatible with what we saw. You'd also expect the engines to recover pretty quickly as it leveled off.

The limitations at high altitude are primarily air/volatiles degassing out of the fuel. That's not going to be much of an issue at sea level, even if the engines are a bit higher up during rotation.
APU is a nice-to-have; it's on the MEL. If you lose all four generators, it's because of some major carnage in the electrical software/hardware and chances of putting the APU on line even if it's operating are very slim.

Many are maintenance or production test flights. Someone commented upthread that every Boeing widebody built gets the RAT deployed on its first flight, and I imagine some maintenance procedures require it too.

ASN has a section on electrical power incidents: https://asn.flightsafety.org/asndb/cat/ACSE

In particular try these:

https://assets.publishing.service.go...009_G-EZAC.pdf
https://asn.flightsafety.org/wikibase/233343
https://asn.flightsafety.org/wikibase/219748
https://asn.flightsafety.org/wikibase/34357

You overlooked that they (the pilots) were trading speed for range/time. The aircraft slowed down by around 50kts while gliding. That is a lot of extra energy to use for range. It's visible in the video that the AoA slowly increases during the glide (I don't mean the flare at the end).

There is easily-correctable available data with the aircraft's altitude at pretty much the end of the runway and it is not at 200 feet (it's around 100\xb112.5 feet).

As the aircraft visibly continues to climb past that height (and for a longer period than ADS-B data covers, if the camera's perspective casts doubt on that), it seems rather clear to me that it reached its peak height past the end of the runway.

In light of this I find the fact that people keep calculating a glide from the runway to the crash site to be a bit strange. Wouldn't the first step of any math be to try to determine where it started descending?

Thanks - I'm pretty sure that I read all the posts in both threads but missed that calculation as to the height at the end of the runway. I had originally guessed that the top of climb was 1,000 feet beyond the end of the runway (the current location is based on the referenced statement of the rotation point and an assumed ground speed, not air speed, of 180 kts). That still doesn't get the jet to the crash site, particularly if the post I relied on that it was 50 feet below the runway is incorrect. As far as the benefit of trading speed for distance, there wasn't that much extra speed to start with relative to the likely maximum L/D speed for that configuration and any slowing below it will reduce distance, not increase it, except of course for breaking the glide, i.e. flare at the end (there may have been a little benefit in rounding off the transition from climb to glide that I didn't take into account but I think it was small). My estimate for L/D based on known comparables that didn't include the RAT was actually 12, not 13, and I assumed that they were flying at the max L/D airspeed for that configuration even though it's likely that the crew didn't know what it was (and neither do I) but were following the prime directive, "don't stall". I also didn't take into account the headwind, which would reduce the maximum L/D available and require a slightly faster airspeed to make good than for no wind.

Thanks for the clarifications

My question is then: what is the minimum loss of thrust in both engines (perhaps more relevantly expressed as a % in fuel flow reduction from expected) that could produce the profile we saw. I appreciate this is a figure with many variables including timing and rate of loss.

The reason I think this question is relevant is because we pretty much have 2 prevailing theories at this point:

1. A failure, or reduction of thrust (below idle, indicated by loss of AC generators), that somehow impacted both engines, within 20s of rotation (explaining the RAT and gear orientation)
2. Somehow a loss of all AC power, leading somehow to a reduction of thrust or failure of engines (both engines impacted identically is assumed in this scenario since all AC is lost), and was of course below the minimum thrust needed to fly with gear down at this weight and temperature

I agree that if it is completely infeasible that loss of all AC power could do anything but cause thrust reduction of X where thrust minus X is not enough, even with gear down in high temperature and significant weight at the critical moment of takeoff to cause the profile we saw, then theory 2 is invalidated. I would love to invalidate any of the theories here but I do think some specific calculations, simulations or test data is needed

L/D of 12 would have needed the aircraft to be at 270' 1km out, 13 needs 250'.

The cctv neither confirms nor denies that top of climb could be as high as 270'. My 1km/200' estimate was conservative. I guessed 160kt average over the 7s to allow for the 25007 wind
and some deceleration.

Basically you cannot rule out loss of thrust around the time of loss of electrics.