Ask The Pilot

[ChrisGibbs]

I just noticed that myself. I paxed twice on a 330 this week, and noticed the 'ding', so I asked about it. I think Microsoft would describe it as an 'undocumented feature'. I don't know whether the 380 does it or not.

I'm reasonably sure this feature is on the A380. I'll check on tomorrow evenings QF128 service. I can't recall seeing it on the A32x.

 

[jb747]

But I can just about always, in the seat of my pants, detect when descent has begun. I guess that means it's more than a degree in pitch. What exactly is happening when you begin your descent? Haul back on the throttles, do something with the control surfaces, punch the autopilot button that says "Sydney"?

We were talking about climbing, not descending.

Your ability to climb is pretty much defined by the margin between the power you need in the cruise, and max power available. At low levels there is a large difference, hence the very steep attitudes that you sometimes see (767s regularly go over 20 degrees). Eventually, of course, there will be no power margin, so the attitude you need for level flight will be as high as you can go.

But, coming down, you aren't limited by power at all. Gravity does all of the work. So, on the way down, your pitch angle is limited by the maximum or target speed. If the aircraft is clean, then you probably won't go below about minus 2.5 degrees. With the speed brakes extended, and at maximum airspeed, that could be as low as minus 10 degrees. Most descents, at normal target airspeeds, are at attitudes of zero to minus one degree.

So, climbing at altitude, you have a very minor power change ('cos there isn't much power margin), and a pitch change of perhaps a degree. Coming down, the engine power is reduced to idle (so a very large change), and the pitch is reduced by about 3 or 4 degrees....so there is much more to notice. Straight and level flight at cruise is about +2.5 degrees.

Over the years, you will have been on board for innumerable descents that you didn't notice...when a small change, or very early descent was requested, and a descent rate of something like - 500 fpm was selected. The power reduces by a couple of %, and the pitch by about a degree.

 

[chrisb]

The Airbus has a memory procedure for 'loss of braking'. The Boeings (747/767 anyway) don't.....
.

Out of interest, can you provide a quick summary of that procedure?

Thanks.

 

[Skyring]

But, coming down, you aren't limited by power at all. Gravity does all of the work. So, on the way down, your pitch angle is limited by the maximum or target speed. If the aircraft is clean, then you probably won't go below about minus 2.5 degrees. With the speed brakes extended, and at maximum airspeed, that could be as low as minus 10 degrees. Most descents, at normal target airspeeds, are at attitudes of zero to minus one degree.

Thanks. That (especially the engines to idle bit) explains it perfectly. Reading your posts over time I've been getting the impression that there's often a lot of minor tweaking going on mid flight, and I rarely notice any change in altitude through my seat of pants sensor.

 

[markis10]

One other difference I've noticed when flying on an Airbus is the chimes are activated and the exit signs flash when the gear is either retracted or extended. Is this other feature specific to Airbus?

Thanks

No, the 717 has a similar feature, some aircraft also activate the lights when flap extension takes place as an alternative.

 

[Mal Ware]

Not sure if this has been asked but is there a special code/word pilots use if under duress in the coughpit to alert the atc covertly? Also if so, is it international or does each country manage their own?

Of course I am not asking you to say it here, just curious if there is such a thing?

 

[markis10]

Not sure if this has been asked but is there a special code/word pilots use if under duress in the coughpit to alert the atc covertly? Also if so, is it international or does each country manage their own?

Of course I am not asking you to say it here, just curious if there is such a thing?

There may or may not be one or more than one (not trying to be flippant, it would in actual fact be an offence to answer that question for me under Part IV of the Crimes Act, Official Secrets and Unlawful Soundings).

 

[jb747]

Out of interest, can you provide a quick summary of that procedure?

Reverse thrust - Max
Brakes - Release
Anti skid - Off
Brakes - Apply

If that doesn't work

Park brake - On

 

[jb747]

No, the 717 has a similar feature, some aircraft also activate the lights when flap extension takes place as an alternative.

Actually I misread the original question...thinking about something else.

The signs have an automatic function, so they'll come on with any flap extension, or l/g selected down.

 

[MEL_Traveller]

A friend of mine who is cabin crew explained the 'ding' and extinguishing of the exit sign means 'gear up' and the same in reverse... the ding and illumination of the exit signs indicates gears down. It will necessarily occur almost immediately after takeoff, but sometime out before landing.

They were unable to answer why however... (what is the purpose of it?). Does it indicate an exit door is no longer operable (because the pressure is such that it can't be opened at that point (on takeoff)) and in reverse, does it mean the exit is operable from the time the sign illuminates? Or is it simply an audible and visual reminder to pax to make them aware of where their exit might be if they need it?

 

[maroonone]

What a great thread = only 3 nights of ignoring my spouse (woops) and all 259 pages read. Thanks to all.

 

[jb747]

A friend of mine who is cabin crew explained the 'ding' and extinguishing of the exit sign means 'gear up' and the same in reverse... the ding and illumination of the exit signs indicates gears down. It will necessarily occur almost immediately after takeoff, but sometime out before landing.

That's not what the manual says it does. When selected to auto, the seat belts illuminate (and there's the ding), when the landing gear is selected down, and/or the slats are extended. The signs go out when the opposite conditions are fulfilled.

But, there's the ding that happens just after lift off, and which seems to correspond with the gear being selected up.

They were unable to answer why however... (what is the purpose of it?). Does it indicate an exit door is no longer operable (because the pressure is such that it can't be opened at that point (on takeoff)) and in reverse, does it mean the exit is operable from the time the sign illuminates? Or is it simply an audible and visual reminder to pax to make them aware of where their exit might be if they need it?

I actually don't think it does or means anything. It seems like a bug to me. What I think is happening is that the gear selection up, momentarily fulfils the 'off' condition, and then it realises that the slats are still extended, so it goes back to the 'on' condition. There is no reference to it that I can find in my manuals.

Random 'dings' are a bit of an Airbus feature. We were getting random triple dings for a while, but one of the later software mods seems to have corrected that.

Anyway, I'll put the question of the post liftoff 'ding' to one of the experts at work, and we'll see if there is a real reason.

 

[oz_mark]

A friend of mine who is cabin crew explained the 'ding' and extinguishing of the exit sign means 'gear up' and the same in reverse... the ding and illumination of the exit signs indicates gears down. It will necessarily occur almost immediately after takeoff, but sometime out before landing.

I was once told it was a hangover from when the no-smoking signs were used. The dings corresponded to them going on and off, but it's been that long since I was on a flight that allowed smoking that I don't know when those signs went on and off. Anyhoo, something called CIDS is apparently what causes the ding.

 

[ChrisGibbs]

But, there's the ding that happens just after lift off, and which seems to correspond with the gear being selected up.

JB - this is the gear up "ding" I was referring to in my original post. On an A330 it can also be heard when gear down is selected. In the last couple of weeks I've done QF, RJ, CX and KA on A330's and they all exhibit the same "feature" which would indicate a similar version of software. Both "dings" also coincide with the EXIT signs flashing. This is not to be confused with the SEAT BELT signs flashing when either the flaps or gear is extended. As stated previosuly I'll check later tonight if this undocumented feature also exists on the 380's.

 

[MEL_Traveller]

That's not what the manual says it does. When selected to auto, the seat belts illuminate (and there's the ding), when the landing gear is selected down, and/or the slats are extended. The signs go out when the opposite conditions are fulfilled.

But, there's the ding that happens just after lift off, and which seems to correspond with the gear being selected up.



I actually don't think it does or means anything. It seems like a bug to me. What I think is happening is that the gear selection up, momentarily fulfils the 'off' condition, and then it realises that the slats are still extended, so it goes back to the 'on' condition. There is no reference to it that I can find in my manuals.

Random 'dings' are a bit of an Airbus feature. We were getting random triple dings for a while, but one of the later software mods seems to have corrected that.

Anyway, I'll put the question of the post liftoff 'ding' to one of the experts at work, and we'll see if there is a real reason.

two separate things. I'm only talking about the EXIT signs - they extinguish and illuminate when gear goes up and down. This is accompanied by a ding as the sign goes out/comes on. It is not a bug. I can't confirm for the A380 because I've never been in a position to see an exit sign! But for all others that is standard (A320 onwards at least - it's been so long since I've been on an airbus classic A300 or 310 I can't remember).

The seat belt sign obviously stays illuminated during these phases of flight and separate ding accompany those as they are turned on and off.

Because the EXIT sign extinguishes immediately on gears up, and comes on again once the wheels are locked down, i wondered if that referenced whether pressure was such that the exit was now usable... or whether it was just a ding to draw attention to the exit for pax.

 

[MEL_Traveller]

JB - this is the gear up "ding" I was referring to in my original post. On an A330 it can also be heard when gear down is selected. In the last couple of weeks I've done QF, RJ, CX and KA on A330's and they all exhibit the same "feature" which would indicate a similar version of software. Both "dings" also coincide with the EXIT signs flashing. This is not to be confused with the SEAT BELT signs flashing when either the flaps or gear is extended. As stated previosuly I'll check later tonight if this undocumented feature also exists on the 380's.

its actually gear locked down i think (as opposed to just gear down selected).

 

[jb747]

I was once told it was a hangover from when the no-smoking signs were used. The dings corresponded to them going on and off, but it's been that long since I was on a flight that allowed smoking that I don't know when those signs went on and off. Anyhoo, something called CIDS is apparently what causes the ding.

The 'no smoking' signs/switch still exist. The switch is mostly just left in the on position. The automatic function, if used, operates them with the same triggers as the seat belts, i.e. slats or gear.

CIDS means 'cabin intercommunication data system'. Whilst I'm sure it's the source of all of the dings and bongs, I'm not convinced of the particular relevance of this particular chime. I've just sent off an email to the tech people, so I'm sure I'll get an official response sooner or later.

 

[jb747]

its actually gear locked down i think (as opposed to just gear down selected).

No. It's landing gear 'not locked UP' in the Boeing wording, and Airbus, 'landing gear extended'.

It doesn't have to be locked down...just any form of not completely retracted.

 

[jb747]

My books (!) are devoid of an explanation. There are things that happen automatically at the doors, but they don't explain the noises. There is a pressure differential measurement, but it has its own warning light, and there is also a mechanical lock. It could possibly be related to that, but if so it operates at different points to the 380.

It may be in the cabin crew manual...they do have some secret information. Our million page book covers doors in about 2 pages.

 

[MEL_Traveller]

No. It's landing gear 'not locked UP' in the Boeing wording, and Airbus, 'landing gear extended'.

It doesn't have to be locked down...just any form of not completely retracted.

well, whatever the term is, the exit sign does not illuminate until the gear is down and I think stops extending (the sign does not come on as soon as the gears start to go down cause you can hear the noise from the airflow and that's not when the sign comes on)