RobertL18C wrote:
Will check next time I see an A320 colleague – full flap produces a lower angle of attack for the approach, and lower sight picture so perhaps higher risk of submarining on touchdown? Also either ditching recommends a smaller flap setting, or it was a crew decision based on their knowledge/expertise?
The report discusses this. It implies that perhaps going to full flap was advisable but says that the decision was reasonable. Sully said he thought flaps 2 would give him more energy to allow a flare.
Yes but it wouldn’t have been possible to stall the Airbus anyway, as far as I know there was no degradation to Alternate law?
This is true. The only reason Normal law was available is that they started the APU immediately after the bird strike so had enough electrical power. This could in fact have been critical as apparently the aircraft was flown well below green dot speed for most of the time after the strike.
If anyone wants to visit the real thing, it is in a museum now
JasonC wrote:
This could in fact have been critical as apparently the aircraft was flown well below green dot speed for most of the time after the strike.
Very interesting because this is a point that was emphasized by Sully in the movie too as critical, in the context of skipping directly to APU rather than waiting until getting to it in the checklist (item 15 if I recall correctly)…
chflyer wrote:
Very interesting because this is a point that was emphasized by Sully in the movie too as critical, in the context of skipping directly to APU rather than waiting until getting to it in the checklist (item 15 if I recall correctly)…
Yes particularly as he thought he was flying at or above green dot but the data showed he wasn’t. Clearly he was quite overloaded but a good reminder that under pressure we may not fly the speed we want to fly particularly when doing other tasks at the same time.
Not sure people are familiar with green dot Jason.. I think the only plane I ever saw one was yours (and had never heard the concept before). Even then at first I got confused as for me Vref is related to landing but it was shown on climb too.
1.3x stall speed in the current configuration, was it? (Or is it landing?)
I saw the movie – very good.
Green dot speed in an A320 is ‘best L/D ratio’ and is calculated by the computer like this:-
Gross Weight (in tonnes) + 85 + 1 kt per 1000 feet above 20k.
The NTSB report says the weight at the time of the accident was estimated at 150000lbs so that means the green dot speed would have been 153kts
stevelup hopefully an Airbus pilot pops in, but the rule of thumb is 2 times ATOM (aircraft take off mass) in tonnes plus the effect of compressibility on stalling angle of attack as you go above Mach .5 – this is best L/D speed and suggests at 68 tonnes this speed would be closer to 220 KIAS.
The ATPL performance exam, which uses an Airbus as a proxy, talks of green dot as the speed for best angle of climb one engine inoperative OEI.
…here is link to the NTSB report
https://www.ntsb.gov/investigations/accidentreports/pages/AAR1003.aspx
Starting the APU immediately seems to me the most logical think to do, item 15 is a nice movie touch I think :-). Losing both engines means two generators are gone. Basically you power the avionics on batteries. This means Single EFIS and ECAM screens..a lot of system degradation. So powering up the APU gave back a lot of system info to make the right decisions…..
