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jessman
Topic Author
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Could Autopilot Descend When Pressure Drops?

Tue Aug 16, 2005 7:20 am

With the passengers on the Helios flight apparently freezing and the crew apparently incapacitated, I wonder if the autopilot could or should be programmed to descend to an altitude where people could breathe and not freeze to death.

So, would such a modification to autopilot technology be feasible
 
star_world
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RE: Could Autopilot Descend When Pressure Drops?

Tue Aug 16, 2005 7:22 am

Technically, yes... however would it be practical in busy airspace where having a computer-determined descent like that could cause chaos with other aircraft in the vicinity? I'm not sure any ATC group would be too happy about aircraft descending to a predetermined altitude by themselves without their knowledge...!
 
captaingomes
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RE: Could Autopilot Descend When Pressure Drops?

Tue Aug 16, 2005 7:24 am

If I am not mistaken, the FBW Airbuses do it automatically. How they avoid any high terrain I don't know, but hopefully somebody more knowledgeable can answer.
"it's kind of like an Airbus, it's an engineering marvel, but there's no sense of passion" -- J. Clarkson re: Coxster
 
AirRyan
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RE: Could Autopilot Descend When Pressure Drops?

Tue Aug 16, 2005 7:28 am

Let's just say the Boeing autppilot even on the 737-300 series aircraft is a matter of turning the dial to 10000 and pressing the FLCH button. They could squak 7777 if need be, but that's one of the very first things I'd be looking to do, especially with the incident of Payne Stewart and this in my mind. I'll contact ATC on my descent - if I get a chance before I pass out.
 
PhilSquares
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RE: Could Autopilot Descend When Pressure Drops?

Tue Aug 16, 2005 7:34 am

Quoting Captaingomes (Reply 2):
If I am not mistaken, the FBW Airbuses do it automatically

No, the FBW Airbuses don't do that.
Fly fast, live slow
 
captaingomes
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RE: Could Autopilot Descend When Pressure Drops?

Tue Aug 16, 2005 7:36 am

No, the FBW Airbuses don't do that.

Ok sorry about that then. I was once told they did, but I didn't have any way of verifying it.
"it's kind of like an Airbus, it's an engineering marvel, but there's no sense of passion" -- J. Clarkson re: Coxster
 
AGM114L
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RE: Could Autopilot Descend When Pressure Drops?

Tue Aug 16, 2005 8:13 am

Do airlines utilize radar altimeters at all?
My Boeing can blow up your Boeing
 
Bobster2
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RE: Could Autopilot Descend When Pressure Drops?

Tue Aug 16, 2005 9:26 am

In theory, the autopilot could use GPS to check for safe altitude and direction in order to not fly into a mountain. In theory, the autopilot could call ATC to clear everybody out of the area.
"I tell you this, no eternal reward will forgive us now for wasting the dawn." Jim Morrison
 
air2gxs
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RE: Could Autopilot Descend When Pressure Drops?

Tue Aug 16, 2005 10:04 am

Quoting AGM114L (Reply 6):
Do airlines utilize radar altimeters at all?

The correct term is radio altimeter and yes airliners do use them. They become active at 2500 feet.

Quoting AirRyan (Reply 3):
Let's just say the Boeing autppilot even on the 737-300 series aircraft is a matter of turning the dial to 10000 and pressing the FLCH button. They could squak 7777 if need be, but that's one of the very first things I'd be looking to do, especially with the incident of Payne Stewart and this in my mind. I'll contact ATC on my descent - if I get a chance before I pass out.

In the time it takes to do that, I'd have my mask on. When I was learning to fly, my instructor always said "fly the airplane first, unless you're about to die. Deal with that and then fly the airplane." It was tongue in cheek, but that lesson stayed with me.
 
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HAWK21M
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RE: Could Autopilot Descend When Pressure Drops?

Tue Aug 16, 2005 4:38 pm

Yes.A Modification could be done.But As star_world said will lead to further confusion.
I think a remedy after this Accident could be to ensure that Pilots keep their O2 masks on for most period of time.Uncomfortable but Safe.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
T prop
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RE: Could Autopilot Descend When Pressure Drops?

Tue Aug 16, 2005 4:44 pm

Bombardier's Global Express with it's advanced avionics will fly itself down to lower altitudes in the event of a depressurisation.

A friend of mine is a flight mechanic on one of these and he recently took me on a tour of a brand new one. Amazing airplane!


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pilotaydin
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RE: Could Autopilot Descend When Pressure Drops?

Tue Aug 16, 2005 10:53 pm

im pretty sure the G5 has a feature called auto descend, it drops to below 15K as i recall in the event of a depr.
The only time there is too much fuel onboard, is when you're on fire!
 
air2gxs
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RE: Could Autopilot Descend When Pressure Drops?

Wed Aug 17, 2005 12:07 am

Quoting HAWK21M (Reply 9):
I think a remedy after this Accident could be to ensure that Pilots keep their O2 masks on for most period of time.Uncomfortable but Safe.

That would require a major change to the certification of all aircraft. As I recall, the flight crew must have something in the area of 45 minutes of supplemental oxygen. Unless the mask is operated in diluter demand for the whole flight. I don't dee the flight crews going for it just because of 1 accident.
 
Mir
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RE: Could Autopilot Descend When Pressure Drops?

Wed Aug 17, 2005 4:24 am

Quoting Star_world (Reply 1):
Technically, yes... however would it be practical in busy airspace where having a computer-determined descent like that could cause chaos with other aircraft in the vicinity? I'm not sure any ATC group would be too happy about aircraft descending to a predetermined altitude by themselves without their knowledge...!

The altitudes at which a pressurization failure would be a big problem that needs addressing right away aren't really that busy. When people's lives are on the line, ATC would just have to deal with it. If the autopilot put 7700 into the transponder automatically, ATC would know that there was something wrong, and they probably have set procedures for dealing with that sort of thing.

Quoting Air2gxs (Reply 8):
Quoting AGM114L (Reply 6):
Do airlines utilize radar altimeters at all?

The correct term is radio altimeter

Are you sure about that? I've heard it both ways. It may be an international difference.

-Mir
7 billion, one nation, imagination...it's a beautiful day
 
air2gxs
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RE: Could Autopilot Descend When Pressure Drops?

Wed Aug 17, 2005 7:41 am

Quoting Mir (Reply 13):
Are you sure about that? I've heard it both ways. It may be an international difference.

Positive, I believe we had a discussion about that several months ago. If I recall, it really is just a difference in the frequency band used, but all airvraft I have ever worked on call it a radio altimeter.
 
AGM114L
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RE: Could Autopilot Descend When Pressure Drops?

Wed Aug 17, 2005 7:51 am

Quoting Mir (Reply 13):
Quoting Air2gxs (Reply 8):
Quoting AGM114L (Reply 6):
Do airlines utilize radar altimeters at all?

The correct term is radio altimeter

Are you sure about that? I've heard it both ways. It may be an international difference.

-Mir

MD/Boeing use the term radar altimeter. I'm no expert on the electromagnetic spectrum but I always associated radio waves with commo, and radar for dist/el/az...
My Boeing can blow up your Boeing
 
air2gxs
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RE: Could Autopilot Descend When Pressure Drops?

Wed Aug 17, 2005 7:54 am

Quoting AGM114L (Reply 15):
MD/Boeing use the term radar altimeter. I'm no expert on the electromagnetic spectrum but I always associated radio waves with commo, and radar for dist/el/az...

No, in fact Boeing uses the term Low Range Radio Altimeter (LRRA) on the B747 and radio altimeter on the other aircraft. When I return to work tomorrow I can get you the appropiate AMM references.
 
AGM114L
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RE: Could Autopilot Descend When Pressure Drops?

Wed Aug 17, 2005 8:02 am

Air,

I'm looking at a 64D operators manual right now, TM 1-1520-2541-10 pg. 3-3. Boeing clearly calls it the AN/APN-209 Radar Altimeter.

Must be different on the airliners.

[Edited 2005-08-17 01:02:58]
My Boeing can blow up your Boeing
 
FredT
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RE: Could Autopilot Descend When Pressure Drops?

Wed Aug 17, 2005 5:09 pm

The difference lies in the mode of operation. A radar emits a pulse which bounces back. The time it takes the pulse to bounce is timed, giving a distance as you know the velocity of the pulse.

A radio altimeter does not emit a pulse. It emits a continuous signal with a triangle wave frequency modulation. The returned signal is mixed with the emitted wave, causing a beat frequency proportional to the difference. The difference is proportional to the time the returned signal spent in transit which, again, gives the distance as you know the velocity of the radio signal.

Some aircraft, mainly military, do have altitude radars which operate by emitting a pulse. The AH64D is likely amongst those.

[Edited 2005-08-17 10:10:44]
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
abbs380
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RE: Could Autopilot Descend When Pressure Drops?

Thu Aug 18, 2005 5:02 pm

I've got to go with Air2gxs. Its a LRRA, and has been since at least the 741 days. Don't know about 64/D, military has there own system.
 
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HAWK21M
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RE: Could Autopilot Descend When Pressure Drops?

Fri Aug 19, 2005 12:47 am

Quoting Air2gxs (Reply 12):
That would require a major change to the certification of all aircraft. As I recall, the flight crew must have something in the area of 45 minutes of supplemental oxygen. Unless the mask is operated in diluter demand for the whole flight. I don't dee the flight crews going for it just because of 1 accident

Agreed.Also We still dont know what exactly went wrong.

Quoting Mir (Reply 13):
I've heard it both ways. It may be an international difference.

Out here its reffered to as LRRA [Low range Radio Altimeter].
regds
MEL
I may not win often, but I damn well never lose!!! ;)

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