View Full Version : Pressurisation non normal sequence of events NG
Pin Head
8th May 2016, 15:51
Hi
Please can you advise the sequence of events in the event of a dual engine failure and a complete loss of electrics. (Before APU start or APU U/s)
Apart from the manual controller which is on The battery bus everything else is on AC.
Kind regards
Pin
galaxy flyer
8th May 2016, 16:03
I didn't know the 737 was known for double engine failures. I'd guess, the manual controller would try to close the outflow valves while the pilots did the heavy lifting of STARTING THE APU, followed by starting an engine or two. Far more important than the pressuriation problem.
GF
Pin Head
8th May 2016, 16:44
Wells there's a NNC for losing your two power plants so it is possible.
Yes. I know about priorities.mbut just want to know !
I'd guess, the manual controller would try to close the outflow valves while the pilots did the heavy lifting of STARTING THE APU,
As far as I know, manual is only controlled by the pilots using battery power (no main bus DC power available). During a dual engine failure (prior to APU start), the outflow valves will remain in their last position. If the outflow valves (in the frozen position) happened to be letting out more air than required then the cabin will start to depressurise. Since there will be no power to the "auto" motors, I would say that the 14000' backup function of the "auto" motors would not work. There is no 14000' backup function in the "manual" motor.
Apart from the manual controller which is on The battery bus everything else is on AC.
Techincally speaking, the controllers and auto outflow valve auto motors run on main bus DC, but I understand your point... AC is required to generate the main bus DC.
Simply select MANUAL and use the OPEN/CLOSE switch to control the outflow valve!
EW73
B737900er
11th May 2016, 08:19
Isn't this covered in any of your sim cycles?
flyingchanges
11th May 2016, 13:24
With no bleed air, how much difference is it really going to make?
I would focus on other more pressing matters.
With no bleed air, how much difference is it really going to make?
It would be interesting to find out how much bleed air a windmilling engine produces. If it is producing enough pressure to open the required valves, then closing the outflow valve more should assist in maintaining cabin pressure.
Anyway, one thing at a time. Let the warnings and cautions dictate your actions as they arrive.
plhought
12th May 2016, 13:40
It would be interesting to find out how much bleed air a windmilling engine produces. If it is producing enough pressure to open the required valves, then closing the outflow valve more should assist in maintaining cabin pressure.Sweet f*** all unfortunately. There isn't even enough air to operate the bleed air regulator & PRSOVs on the engine.
Throw the O2 on get the plane safe. Let the back have a little hypoxic-induced sleep whilst ya fly her down (I suspect it'll be coming down pretty good on it's own with a simultaneous dual engine failure).
flyingchanges
12th May 2016, 14:40
Maybe the windmilling engines could also produce enough thrust to maintain altitude.
No need to be sarcastic.
It was a question, not a response.
What are N1/N2 values in a controlled descent?