737 Stall Test

[B737NG_Pilot]

The stall warning test requires that AC transfer busses are powered for up to 4 minutes. Why 4 minutes?

[flyboyike]

Because three is not long enough and five is much too long.

[TURIN]

Now, that is more like it flyboy.
Like it. :-)

[flyingchanges]

Takes a while for the vacuum tubes to warm up. Yesterdays technology today...

[oceancrosser]

Oh, they still make airplanes that require the stall warning to be tested before flight?

[RAT 5]

Oh, they still make airplanes that require the stall warning to be tested before flight?

You can test many things, but is it necessary? I flew for many airlines who tested these on B737's, because you could, I suspect; or was it standard Boeing? They did not test everything, but did include the FDR & over speed clackers, but not the CVR? Again I suspect these are no-go items.
I know teach for a company who have just stopped testing stall warners and overspeeds, but do test the VOR/ILS each new crew. You figure it out.

There's nowt so queer a folk, but what do other airlines have as SOP's? And why?

[Kefuddle]

The test is the normal procedure for the prelim pre-flight, so it is tested first flight/every crew change.

[tdracer]

It takes several minutes after a cold power up for the Inertial Reference Units to stabilize and align. I don't know if the 737 Stall Warning uses the IRS but it would explain the 4 minutes if it does....

[Denti]

No, it doesn't need the IRS, however the other subsystems like the Stall Management / Yaw Damper Computer need a couple minutes to run through their respective BITE tests as well.

[172_driver]

I tried this the other day, cold & dark plane.. put in on GND PWR and went for the stall warning test. Seemed to work fine? They were purring like a pussycat.

Note: The stall warning test requires that AC transfer busses are powered for up to 4 minutes (my bold)

Perhaps it means a maximum of 4 min, but it could go faster?

[ajd1]

I think that Denti might be on the right track in that the SMYD computers might be involved in the 4min requirement. Anyway, I've asked a bloke wot knows about 737 wiggly amps etc to find out. I'll be back.

[captjns]

No mention on 27-32 of the Mx. Ref. Man. About a 4 minute warm up time. The manual does state if during the test, the control column shaker operates until you release the test switch, or a maximum of 20 seconds. The 20 second maximum time limit prevents damage to the control column shaker motor. The stall warning test is inhibited when the airplane is in the air.

[RAT 5]

Over the years I have accumulated various QRH queries, but not found a technical pilot who could answer them, nor who followed them up to Boeing. I tried Boeing direct and was shunted back to 'your technical pilot'. Is anyone here willing to have a stab at answering them? It's not a mega list, <5. It might throw up some interesting thoughts & facts. From such round table discussions Boeing have altered things in QRH.

I've flown for various companies who asked Boeing to alter some checklists to suit the airline philosophy, and they obliged. Thus there are different ways of doing the same thing. I've since had contact with another operator via sim teaching who has altered the same QRH pilot actions in a different way to my previous experience, both of which are altered from standard Boeing. I wonder how many more versions there are out there.

But that in fact is a different topic to what my initial quest is: to understand why certain actions are required in certain scenarios. Any volunteers?

[flyboyike]

I'd volunteer, but I'm not smart enough. Well, that and I don't fly a Boeing. In my Bombardier time I've witnessed airlines perform some procedures in diametrically opposite ways all the while claiming that performing them in any manner other than their own would result in major calamities.

[B737NG_Pilot]

Thanks Denti & 172_driver.

I did check with the technicians on the 737NG in my company. As per them it takes a few minutes for the all systems to boot up, after AC power is applied.

Also as Denti mentioned, the word is up to.

Thanks