Emergency Descend 737NG

[Olendirk]

Guys,

question: why does boeing mention first speed brake then throttles idle than do the modes in the AP. Isnt it logic to put first the altitude with lvl chg and then do the speedbrakes and the throttles? The Throttles would come forward again doing the speedbrakes out without desceding, what do you think?

Seeya

OD

[Ennie]

Our procedures are as you mention, Alt first, lvl change, throttles back, speed brake, set speed.

According to some people at work we are changing to some Boeing procedures early next year so maybe this will be one of the changes, so I'll find out then!

[captplaystation]

Even bigger mystery to me has been why we don't drop the gear for emerg descent. ROD goes ballistic ( which is after all the whole point of the exercise ). and you can do MMO/320 if memory serves me well. Just have to remember to slow down a little before you retract it if you want to present the next crew with a complete aircraft.

[mustafagander]

Capt PS, think gear max extend speeds.

On the big Boeings it can be well below min speed in crz. Almost invariably there will be a level deceleration segment while the pax are all getting hypoxic. Boeing produced graphs - published in the FCTM - showing that, while the gear down option gets you to F140 in a little less time, only seconds, the gear up Vmo option gets you into the low 20s quicker. Hence probably less traumatic for the pax.

What if you are 3000 miles from the nearest bit of useful dirt and the reason for the emergency descent is airframe damage? Would you have the ba!!s to extend the gear and hope it will retract? Are you a good swimmer?

[captplaystation]

I agree if you are over the sea with a long way to go (or suspecting structural problems exist ) no way. 737NG extend speed is 270KIAS which is below our typical IAS in cruise so if the only problem is getting down I think the gear ( in a 737 short-haul scenario) makes an excellent idea. Don't think you have to worry about extra noise / buffeting upsetting the pax, they will be pretty upset anyhow by whatever demanded the emerg descent )

[Right Way Up]

Capt PS,
The problem with lowering the gear is in most cases you have to decelerate which will keep you in the most dangerous levels of the atmosphere for longer. I am also a firm believer that in this scenario the simpler the procedure the more consistent the results will be. I do not believe the sim prepares you for the reality and stress of a rapid depressurisation.

[alexban]

our manouvers are :altitude set in mcp,push lvl chg,throttle close,speed brake up. This are also Boeing manouvers as you may see in FCTM 7.5.
Also ,Boeing says that rapid descent is usually made with gear up.However ,when structural integrity is in doubt,and airspeed must be limited,extension of the landing gear may provide a more satisfactory rate of descent.(FCTM 7.7)
So,as you see,it's all in the books.All you need to do it's read them carefully.