what speed when both engines fail
 

What speed to use when both engines fail and you have to drift down in a B737

It must be cold up there in Minnesota to be pondering that. Maybe any speed above clean min naneuvering clean would work depending on where you decided to land. Ask Sully.

from the classic QRH from my company;


At or above FL270, set airspeed to 275 knots.
Below FL270, set airspeed to 300 knots.

below fl100 i would start to reduce towards min clean.

hope this helps.

V clean above FL200 for stall margin, Vp clean below FL200 is used in my airplane for drift down on one engine. If both went silent, I would use V clean if clean, and Vp for whatever config I have.

/Rookie

I have always thought that the best L/D speed is achieved at approximately 1.6Vso, but I'm not sure I can document the reasoning.

That is equal to Vclean, which is 1.5 Vso!

Love the restart idea though... :O

To make numbers simple:

Above FL100 = 280kts
Below FL100 = Fup speed

Dont forget to be configured!!!

Regards

B737-800W

OK465, I'm with you. Windmill relight until I've got some air then assist after that.

Why not just follow the loss of thrust on both engines checklist? Says in step 5 in mine for the 737NG:

At or above FL270 set airspeed 275knots. Below FL270, set airspeed to 300knots.

However, below FL100 i would start looking where to set it down and slow down to up speed.

Depends what you want to achieve. Don't you have a QRH?

Denti,

i agree 1000000%, follow the QRH.:ok:

The numbers that i said before are just some figures to have at the back of your mind.

The question by our friend was not, what is the best speed for a windmill start.
The question was about Gliding Speed!!!

Regards

Ah, righto. Best glide should be right at up speed from what i remember, well, probably slightly above.

I think those speeds are to help with engine restart and not to do with the best glide speed. At that stage of the checklist it is assumed that at least one engine will restart. Funny enough the last two options on the loss of thrust on both engines are either one or both engines restart. It mentions nothing about both engines failing to restart:D

I'm retired and haven't flown a big jet for some years but 250kn and sort it out from there flashed up in my head:ok:

Well, if run out of fuel or any abnormal/emergency situation that led to a double engine out without chances to restart, I'd set the Vclean and hope to have a strip within my gliding range (for the B737 Classic, a good rule of thumb is 2.5 x Height)

Check this out, really interesting:

Loss of Thrust on Both Engines

Ciao

RTFQ.

Cost index 0. Best range speed. :ok:

RTFQ?

He says you have to drift down. Why is that a range question? It could just as easily be a terrain question or a don't kill the pax with hypoxia question or many others.

FE, I agree, if your airport is near where you lost both engines get down first then at low altitude use min clean speed until you need to configure for landing. Dead sticking an airliner isn't hard, you just can't get low.

And 275kts at FL370 would be interesting.