VNAV engagement on the 737-300/500

[downwind]

Guys,

What are some view points from 737-300/500 operators on engaging VNAV on their company aircraft?
Is at 400' AGL??? same as VOR LOC/HDG? or 1000 AGL? or at 3000 AGL when you are cleaned up and accelerating to 250 knots?

Do some companys still use the call "BUG UP" at an 2 engine or single engine acceleration altitudes (ie PNF winds up speed selector to 210/220/230 knots)?, or when you engage VNAV this takes care of this procedure?

Thanks DW

[Dualbleed]

At 1500 AGL "flap up speed" ,when flaps retracted VNAV if you want.

[downwind]

hypothetically can you engage VNAV with LNAV/HDG SEL at 400' AGL???

[Blip]

We used to call for VNAV at the acceleration altitude however we don't now because Boeing do not recommend it as there is no flap speed limit protection.

So now we call for "Bug Up" and keep it there until the flaps are up. Then we call for VNAV if we want it.

[Bumblebee]

Likewise we used to select VNAV at Aa...but now call "N1 210/220" - It was okay with the 250kt flap limit speed on the 734, but when we started mixed fleet ops with the 3/500 we had a few instances of flap limit speed exceedances (230kts), so back to the old way again!

[Mr Levitator]

Just a quick q. I was of the understanding that the A/t will give under and overspeed protection when engaged from the #1 ADC. The EFIS 737-3/5 puts red bars from 230 upwards until trailing edges are retracted. The sticky point being leading edges take longer and are still 1/2 to 1/4 extended when the trailing edge are fully in so the 230 red bars drive to Vmo when the LE are still extended.

If this is the case (please correct me if I am wrong) as long as the Trailing Edge AND Leading Edge are monitored as they retract, why not take VNAV strait away?? You can always insert a speed limit for a way point (in the SID or your own) for 210/220kts if you are really worried, but ingeneral if the timing of flap selections is right, the LE transit light will usually go out as you are passing 210 knots (20 knots to spot a problem!) and a smooth continual accel to 250 will have been achived.

Mr L.

[Bumblebee]

I was of the understanding that the A/t will give under and overspeed protection when engaged from the #1 ADC

I think it does....but there's not enough margin on it for it to be reliable at preventing a flap limit speed exceedance. Theoretically it can give you some level of protection but certainly not if it's gusty or a bit bumpy.

Also...

The sticky point being leading edges take longer and are still 1/2 to 1/4 extended when the trailing edge are fully in so the 230 red bars drive to Vmo when the LE are still extended

You more or less answer the question yourself I think!

Ever done an improved climb t/o on a 500? The flaps just don't retract fast enough as you accelerate - and inertia will either take you through 230kts as the auto pilot or FD commands lag so much.

Apparently (according to one of our Trg Standards chaps) one of the other reasons we reverted to using "N1 210/220" was that Boeing themselves queried our SOP's and said that it wasn't what everybody else did.

I for one am quite happy not to use VNAV until clean - It's another slice of swiss cheese in the grand scheme of things and it simplifies our SOPs. Apart from selecting N1, our SOPs for clean up and accel are more or less identical on both single and two engine G/A and EFATO.