Cactus 1549
Thread Starter
Join Date: Oct 1999
Posts: 1,050
Likes: 0
Received 0 Likes
on
0 Posts
Cactus 1549
Hi
Bored on a saturday and watching the movie.
They go on about starting the APU helped them.
My NNC for ditching says APU off. Why and then If it helped them so much why can't Boeing follow Airbus example?
Try and leave the hollywoood spin out of it.
Thank you
Bored on a saturday and watching the movie.
They go on about starting the APU helped them.
My NNC for ditching says APU off. Why and then If it helped them so much why can't Boeing follow Airbus example?
Try and leave the hollywoood spin out of it.
Thank you
Join Date: Oct 2015
Location: KPMD
Posts: 28
Likes: 0
Received 0 Likes
on
0 Posts
By starting the APU and bringing the APU generator on line, the crew of 1549, kept the normal flight control laws (more importantly, the flight envelope protections) available.
This was important, as without auto throttle available (engines flameout) and the neutral speed stability of the C* pitch law, it is not possible to trim to an airspeed. Sully was attempting to maintain green dot (approx max L/D airspeed), but because of the workload and distractions, got slow.
As a result, the last ~200 feet of the flight was on the AOA limiter, which prevented a stall/departure.
However, because he was on the AOA limiter, there wasn't enough energy to flare, which resulted in a hard touchdown and damage to the lower fuselage.
For details, see the NTSB report NTSB/AAR-10/03, specifically the analysis part starting with Section 2.3, Flight Crew Performance.
This was important, as without auto throttle available (engines flameout) and the neutral speed stability of the C* pitch law, it is not possible to trim to an airspeed. Sully was attempting to maintain green dot (approx max L/D airspeed), but because of the workload and distractions, got slow.
As a result, the last ~200 feet of the flight was on the AOA limiter, which prevented a stall/departure.
However, because he was on the AOA limiter, there wasn't enough energy to flare, which resulted in a hard touchdown and damage to the lower fuselage.
For details, see the NTSB report NTSB/AAR-10/03, specifically the analysis part starting with Section 2.3, Flight Crew Performance.
Join Date: Dec 2015
Location: France
Posts: 507
Likes: 0
Received 0 Likes
on
0 Posts
I concur with everything but your second sentence :
He got slow because he pulled some pitch up and even converted some of its kinetic energy into height.
Trimming into an airspeed with a gliding airbus is simple : just do nothing and the aircraft will maintain its pitch angle, speed will then progressively stabilize at the speed which corresponds to this pitch angle.
If this chosen pitch angle is too high then yes, the speed protection will come into play.
The APU is useful in maintaining alive all the electrics and hydraulics. Guaranteeing optimum manoeuvrability.
He got slow because he pulled some pitch up and even converted some of its kinetic energy into height.
Trimming into an airspeed with a gliding airbus is simple : just do nothing and the aircraft will maintain its pitch angle, speed will then progressively stabilize at the speed which corresponds to this pitch angle.
If this chosen pitch angle is too high then yes, the speed protection will come into play.
The APU is useful in maintaining alive all the electrics and hydraulics. Guaranteeing optimum manoeuvrability.
Thread Starter
Join Date: Oct 1999
Posts: 1,050
Likes: 0
Received 0 Likes
on
0 Posts
Ok great stuff.
737 NG NNC for dual engine failure has start APU at item 8, and then off in the ditiching drill.
What does the Airbus say about APU in a ditching situation?
Thanks
737 NG NNC for dual engine failure has start APU at item 8, and then off in the ditiching drill.
What does the Airbus say about APU in a ditching situation?
Thanks
Join Date: Sep 2011
Location: FL390
Posts: 241
Likes: 0
Received 0 Likes
on
0 Posts
Trimming into an airspeed with a gliding airbus is simple : just do nothing and the aircraft will maintain its pitch angle, speed will then progressively stabilize at the speed which corresponds to this pitch angle.
How did starting the APU retain normal flight control law? I haven't read the report but loss of G & Y HYD system will result in ALT LAW.
Join Date: Dec 2015
Location: France
Posts: 507
Likes: 0
Received 0 Likes
on
0 Posts
Oh yes I made a mistake about the airplane maintaining it's pitch angle, it's rather maintaining a flight path since the rule is to maintain a 1G load factor.
If the speed varies, the pich angle will also vary to maintain a 1G load factor.
But the conclusion remains the same :
If your chosen flight path is sufficiently downwards, speed will stabilize around a particular value.
If your chosen flight path is too optimistic relative to the gliding performance.. You will get a speed around Valphaprot or more (but not so stable..)
In the case of cactus1549 I really don't understand why he reduced his speed so much by climbing.
If the speed varies, the pich angle will also vary to maintain a 1G load factor.
But the conclusion remains the same :
If your chosen flight path is sufficiently downwards, speed will stabilize around a particular value.
If your chosen flight path is too optimistic relative to the gliding performance.. You will get a speed around Valphaprot or more (but not so stable..)
In the case of cactus1549 I really don't understand why he reduced his speed so much by climbing.
Note that due to the gear being up, there were no audible altitude call-outs, just "Pull Up! Terrain! Pull Up, Terrain!" Visual judgement was all that was available.
Only half a speed-brake
If anyone's interested let's start a separate thread. I'd happily participate, last time I flexed my brain on this many ends were still loose by the time I had reached my limits. "Why physics does not support Airbus claim to fly level on 1g, and the implications". Or "Why does my Airbus start to climb like crazy with AP OFF on an easterly track south of Gibraltar".
I wish not to hijack this one, just that Fusty's "maintain its current flight path" is as accurate as it gets.
Join Date: Jan 2006
Location: US
Posts: 2,205
Likes: 0
Received 0 Likes
on
0 Posts
Try what? Ditch? Return to LGA? The majority of RTB's to LGA were successful. I think it was 7/8 to rwy 13, 2/4 to rwy 22, and 0/1 to rwy 31.
What's disappointing is the NTSB and Airbus havn't explained to pilots what steps helped, or hindered, the ability to recover the aircraft at LGA.
The NTSB report has the FDR readout. They were below green dot when the bird strikes occurred, got slower, Sully took over and accelerated, and then ultimately slowed to slightly above stall speed despite thinking he was comfortably above Vls. Stress will do that. The FBW protections were a huge part of the successful outcome.
Starting the APU kept them in Normal Law. That kept the AOA protection that was key to a successful outcome. Are you flying a FBW Boeing? Does starting the APU keep your FBW Boeing in Normal Law?
Misd-agin, not only are your figures wrong, but as the NTSB noted, "The immediate turn made by the pilots during the simulations did not reflect or account for real-world considerations."
The sim pilots knowing ahead of time that they would experience a dual engine failure was a huge factor - but not much help in the real world!
