B737-when is it safe to switch off the anti-collision light?

[Menen]

Aircraft stops at aerobridge and starts levers selected to cut-off. Some operators require that the anti-collision light should not be turned off until the engines have run down by 20 seconds - or 20% N2. The idea being that ground staff should not move towards the cargo holds until it is safe to do so.

The ear protectors worn by ground staff don't cut all noise, but simply reduce it to non-dangerous levels. So why can't they listen to the engine noise running down rather than watch for the anti-collision light to stop rotating? Is 20% N2 sufficiently low thrust to prevent someone being blown over?

[BOAC]

It varies with operators. The crucial thing is the speed of the N1 which is the bit that provides most of the suck. In my experience (3 operators) one said 'up to the skipper', one put it off in the normal overhead shutdown scan sequence', the other predicated 5%N1 as 'safe'.
The next difficult bit is to stop the groundcrew approaching even with the light on! Pressure on 20 min t/rounds etc does not help.

[The Greaser]

Presumably 20% is low enough otherwise boeing wouldnt recommend it. Anyway, seems to me at most of our destinations that the handlers generally take no notice of it anyway as in the (frequent) case when we forget to turn it off yet still see airbridge approaching, cargo doors open etc etc!

[TopBunk]

On the 'bus (with the same CFM engines) we use 10% N1 as the point at which the anti-coll is switched off. Seem to remember it was the same on the 737-400.

[TheOddOne]

The next difficult bit is to stop the groundcrew approaching even with the light on! Pressure on 20 min t/rounds etc does not help.

We now conduct several turnaround audits a day (and night) using video and a detailed checklist to trap this sort of practice. If we see something seriously dangerous then we will intervene straight away, of course, but we use the audits to bring unsafe practices to the attention of Handling Agent management. This is then fed back through recurrent training, which we also audit. Hopefully this will produce a better long-term safety culture than simply issuing a bo##ocking on the spot.

This is the practical side of having a Safety Management System. It's not just mumbo-jumbo, but it does take time to work through and have benefit.

Do please leave those belly/top lights on until it's completely safe to approach the a/c. I don't think that relying on someone hearing the engines spool down is a good idea at all! The APU noise is quite sufficient to mask this cue.

Cheers,
The Odd One

[Slightfoot]

Leaving it to the handlers to judge is a bad idea... New people come and go, and might not have the experience to judge wether it's safe or not, and end up as FOD to please the new employer...

What one really needs, is a standardized handsignal for "You left the bloody beacons on again!"

[Menen]

Hand signals. I like the hand signal given by the ground crew to the pilots when clearance is given to pressurise the hydraulic systems in the 737. They bang on the side of the fuselage under the copilots window, prompting him to open the window (if its not raining that is) and peer out. The bloke below then places two fingers into his two eyes (very carefully of course). This means it is clear to "pressyoureyes". Pressurize.....Gitit?

[alexban]

Menen :he,he very nice signal. We also do that,but it is for checking the lights.
About anti-collision light-off below 10% N1 (737).
Usually the ground staff already placed the chokes by then. They tend to be in a hurry.