Jackbr
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How Are Emergency Descents Conducted?

Wed Mar 16, 2011 6:56 am

What are the general procedures for undertaking an emergency descent on an airliner?

Apologies if this question is way too vague, my technical operations knowledge is limited
 
wilco737
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RE: How Are Emergency Descents Conducted?

Wed Mar 16, 2011 7:01 am

Quoting Jackbr (Thread starter):
What are the general procedures for undertaking an emergency descent on an airliner?

Basically, get down ASAP, thrust levers idle, speedbrake extend and with Vmo/ Mmo down to roughly 10-14,000 feet.


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etherealsky
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RE: How Are Emergency Descents Conducted?

Wed Mar 16, 2011 7:47 am

Quoting wilco737 (Reply 1):

Gear/flaps used as well?
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rendezvous
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RE: How Are Emergency Descents Conducted?

Wed Mar 16, 2011 8:02 am

You'd have to slow down a fair bit to use flap - that takes time.
 
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zeke
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RE: How Are Emergency Descents Conducted?

Wed Mar 16, 2011 9:17 am

Quoting Jackbr (Thread starter):
What are the general procedures for undertaking an emergency descent on an airliner?

Oxygen masks on
Establish communications with the other pilot

Start of loop

Select heading and commence a turn off the airway (as traffic maybe below)
Select a lower altitude and commence a descent (this should command the autothrust/throttle to IDLE)
Select the current speed/mach
Check speed, check autopilot/autothrust modes, check commanded thrust level
Select full speed brake whilst monitoring speed
Both thrust levers back to IDLE if the thrust is not at IDLE

The monitoring pilot sits on their hands and monitors these vital actions to ensure the PF gets the aircraft established in the emergency descent safely.

The PF repeats the first loop

Heading okay ? where is traffic/terrain ?
Altitude okay, what height is the terrain ?
Speed, was the aircraft damaged, if it was damaged (e.g. explosive loss of a cargo door) you would keep the indicated speed at the time of the explosive decompression, otherwise, select Vmo/Mmo
Check speed, check autopilot/autothrust modes, check commanded thrust level

The pilot monitoring at the same time as the PF make the second loop
Transmits a mayday call
Turns the engine igniters on
Emergency code on transponder
No smoking/seat belt signs on
Engine anti-ice if required
Lights on
Works through the electronic and/or QRH checklist

Quoting etherealsky (Reply 2):

Gear/flaps used as well?

Gear maybe used in the case of damage, as it will increase drag, normally gear and flap cannot be selected above FL200. Flap would not be used.
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wilco737
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RE: How Are Emergency Descents Conducted?

Wed Mar 16, 2011 10:23 am

Quoting etherealsky (Reply 2):
Gear/flaps used as well?

Nope, All airlines I worked at: Gear and flaps up! The speed needs to be reduced significantly to lower gear and flaps and then you cannot descent with Vmo anymore, you need to use Vle, or the max flap placard speed...
I think only about the 744 where flaps 1 to flaps 5 can take up to 30 seconds. In 30 seconds I have already descended 2000-2500 feet in clean configuration with speed brake extended and Mmo/ Vmo.

Quoting zeke (Reply 4):
normally gear and flap cannot be selected above FL200

They can be used, but it has never been officially certified to use them above 20,000 feet, as there is no normal condition where you need it.

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zeke
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RE: How Are Emergency Descents Conducted?

Wed Mar 16, 2011 2:00 pm

Quoting wilco737 (Reply 5):
They can be used, but it has never been officially certified to use them above 20,000 feet, as there is no normal condition where you need it.

I would not use the word "can", if something is not permitted as it is an aircraft limit, it cannot normally be used.

It could only be used by the Captain if they had the view that the limit has be intentionally exceeded under their emergency authority for the safe outcome of the flight. Otherwise their licence could be revoked, or in worst case, end up in jail for wilful negligence.
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330guy
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RE: How Are Emergency Descents Conducted?

Wed Mar 16, 2011 3:39 pm

I was on a flight a few years ago where we had an emergancy descent over Rotterdam, we were in a Gulf Air A330 going from DUB-BAH... There was a sudden jolt of turbulance that hit the aircraft, It seemed to take forever but in reality it was maybe only 10secs or less before the aircraft pitched down (you all mention throttles to idle but im certian the throttles were opened or power atleast significantly increased) a few moments later (about a minute) the captian came on and apologised for the sudden madness and advised we had hit some extremly strong turbulance and he had to commence an emergancy descent. We descended 7000ft as stated by the captain.
It was a thrilling ride to say the least but next time I think i'd like to know about it before it happens 
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c5load
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RE: How Are Emergency Descents Conducted?

Wed Mar 16, 2011 3:44 pm

What about using inboard T/Rs on four engine airplanes or maybe the t/r on no. 2 on tri-jets?
"But this airplane has 4 engines, it's an entirely different kind of flying! Altogether"
 
330guy
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RE: How Are Emergency Descents Conducted?

Wed Mar 16, 2011 3:56 pm

Quoting c5load (Reply 8):
What about using inboard T/Rs on four engine airplanes or maybe the t/r on no. 2 on tri-jets?

Is it possible to engage the reversers in flight?? always beleived it was not
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travelavnut
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RE: How Are Emergency Descents Conducted?

Wed Mar 16, 2011 4:02 pm

Quoting 330guy (Reply 9):
Is it possible to engage the reversers in flight?? always beleived it was not

It was possible for the DC-8 IIRC.
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ANITIX87
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RE: How Are Emergency Descents Conducted?

Wed Mar 16, 2011 4:06 pm

Quoting 330guy (Reply 9):
Is it possible to engage the reversers in flight?? always beleived it was not

Depends on the aircraft. Concorde was designed to use her T/R in-flight to slow down if needed.

What is the typical descent in FPM that one can achieve during an emergency descent? On a related note, what's the typical nose-down angle for maximum emergency descent?

How much time elapses between the PF thinking, "We need to execute an emergency descent" to the moment when maximum descent rate is achieved?

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Pihero
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RE: How Are Emergency Descents Conducted?

Wed Mar 16, 2011 5:22 pm

Zeke has pretty much written everything to know on a modern airplane.
The only addition, may be, would be to consider a higher Mach /Ias for the descent if there is no structure damage.

Quoting zeke (Reply 4):
Gear maybe used in the case of damage, as it will increase drag, normally gear and flap cannot be selected above FL200. Flap would not be used.

The use of the landing gear was a 741 / 2 / 3 SOP, the captain had a choice of whether use them or not. It allowed a slower IAS / Mach, limited to Vle .
The procedure was awkward as it involved all three flight deck personnel being rather busy. It was cancelled on the 744 on some airlines.
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wilco737
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RE: How Are Emergency Descents Conducted?

Wed Mar 16, 2011 5:29 pm

Quoting zeke (Reply 6):
I would not use the word "can", if something is not permitted as it is an aircraft limit, it cannot normally be used.

Isn't that what I have written? I said, they can be used, but it has never been certified. Basically it is possible. Sure, it is a limitation which has to be observed under normal conditions... But what do I know...

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26point2
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RE: How Are Emergency Descents Conducted?

Wed Mar 16, 2011 5:46 pm

Many newer bizjets have an Auto Emerg Descent feature. Autopilot and autothrottle commences an emergency descent without any pilot input when cabin altitude reaches +24;000' (?). The GLEX descends to and captures 15,000'. The system good if the pilots are incapacitated. I don't know if airliners have this feature.
 
PolymerPlane
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RE: How Are Emergency Descents Conducted?

Wed Mar 16, 2011 6:40 pm

Quoting zeke (Reply 4):
Select a lower altitude and commence a descent (this should command the autothrust/throttle to IDLE)

Do you select descent rate?
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Pihero
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RE: How Are Emergency Descents Conducted?

Wed Mar 16, 2011 6:55 pm

Quoting PolymerPlane (Reply 15):

Do you select descent rate?

No, your descent will be made on :
- idle thrust
- extended speed brakes
- high speed, selected
and all the above will make your descent, i.e your rate of descent, as high as can be.
- to the selected level-off altitude, which is in general FL 100 or MSA if higher.
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26point2
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RE: How Are Emergency Descents Conducted?

Wed Mar 16, 2011 7:39 pm

Quoting PolymerPlane (Reply 15):
Do you select descent rate?

...the plane needs a vertical mode for vertical guidance, FLCH (FL Change) is used. This mode maintains selected speed. Vmo/Mmo.
 
wilco737
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RE: How Are Emergency Descents Conducted?

Wed Mar 16, 2011 7:41 pm

Quoting 26point2 (Reply 17):
FLCH (FL Change

FL CH is the one we use. Then the pitch will be adjusted automatically to maintain Mmo/ Vmo.

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Pihero
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RE: How Are Emergency Descents Conducted?

Wed Mar 16, 2011 8:47 pm

Quoting 26point2 (Reply 17):

...the plane needs a vertical mode for vertical guidance, FLCH (FL Change) is used
Quoting wilco737 (Reply 18):

FL CH is the one we use. Then the pitch will be adjusted automatically to maintain Mmo/ Vmo.

That's for the Boeings;
On the 'Bus, no need to select a mode, the procedures above automatically trigger the OPEN DESCent mode, equivalent to the Boeing FL CH on a descent profile.
I did not want to be type specific.
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474218
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RE: How Are Emergency Descents Conducted?

Wed Mar 16, 2011 11:39 pm

Quoting 26point2 (Reply 14):
Many newer bizjets have an Auto Emerg Descent feature. Autopilot and autothrottle commences an emergency descent without any pilot input when cabin altitude reaches 24;000' (?). The GLEX descends to and captures 15,000'. The system good if the pilots are incapacitated. I don't know if airliners have this feature.


The L-1011-500 (and BA -200's) have a system called Recovery Speed Brakes (RSB). At high altitudes and high Mach numbers the Flight Controls Electronic System (FCES) computers reschedule the spoilers so all 12 spoiler panels are active, in lieu of just 10 active panels on aircraft without RSB. RSB allows the crew to fully deploy the spoilers (with the travel limited on some panels) and not worry about high speed buffeting that could be experience on those L-1011's not equipped with RSB's.
 
vikkyvik
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RE: How Are Emergency Descents Conducted?

Thu Mar 17, 2011 2:18 am

A few questions:

1.) Speed brake use during emergency descent - are they primarily used as spoilers (kill lift thereby increasing descent) or speed brakes (helping prevent the aircraft from overspeeding)? Obviously it will be a combination, but I'm just wondering which is the primary function in this case.

2.) What sort of deck angle will allow you to maintain Vmo/Mmo on idle thrust?

Quoting wilco737 (Reply 5):
flaps 1 to flaps 5 can take up to 30 seconds

Geez! That's only one step of flap setting, right (i.e. there's no flaps 2, 3, or 4)?

Thanks!
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tdscanuck
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RE: How Are Emergency Descents Conducted?

Thu Mar 17, 2011 4:58 am

Quoting wilco737 (Reply 5):
Quoting zeke (Reply 4):
normally gear and flap cannot be selected above FL200

They can be used, but it has never been officially certified to use them above 20,000 feet, as there is no normal condition where you need it.

On some aircraft it cannot be used...the AFM limitation is actually coded into the flap actuation logic, so if you move the handle above 20,000' nothing happens.

Quoting ANITIX87 (Reply 11):
What is the typical descent in FPM that one can achieve during an emergency descent? On a related note, what's the typical nose-down angle for maximum emergency descent?

You can get north of 15,000 FPM (briefly) on some more slippery designs during the initial pitch-over to capture speed. Once you catch up to the Mmo line, you can be over 10,000 FPM. Nose-down angle isn't as vigorous as you might think...maybe 15 degrees initially.

Quoting ANITIX87 (Reply 11):
How much time elapses between the PF thinking, "We need to execute an emergency descent" to the moment when maximum descent rate is achieved?

A few seconds...the highest rate of descent is in the initial pitchover to accelerate to Mmo. Once you're on the Mmo/Vmo curve your rate of descent goes down.

Quoting vikkyvik (Reply 21):
1.) Speed brake use during emergency descent - are they primarily used as spoilers (kill lift thereby increasing descent) or speed brakes (helping prevent the aircraft from overspeeding)? Obviously it will be a combination, but I'm just wondering which is the primary function in this case.

Primarily drag...the whole point of the exercise is to shed energy as quickly as possible.

Tom.
 
wilco737
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RE: How Are Emergency Descents Conducted?

Thu Mar 17, 2011 5:31 am

Quoting vikkyvik (Reply 21):
Geez! That's only one step of flap setting, right (i.e. there's no flaps 2, 3, or 4)?

Yes, the first step where the trailing edge flaps come out. Flaps one is only the inboard and midspan leading edge flaps.

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26point2
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RE: How Are Emergency Descents Conducted?

Thu Mar 17, 2011 9:27 am

Quoting tdscanuck (Reply 22):
You can get north of 15,000 FPM (briefly) on some more slippery designs

An aircraft's certified maximum altitude is determined by its ability to descend to 10,000' in 4 minutes.
 
Speedbird741
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RE: How Are Emergency Descents Conducted?

Thu Mar 17, 2011 1:54 pm

Quoting tdscanuck (Reply 22):
the AFM limitation is actually coded into the flap actuation logic, so if you move the handle above 20,000' nothing happens.

They would extend in the alternate flap mode correct?

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lowrider
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RE: How Are Emergency Descents Conducted?

Thu Mar 17, 2011 2:39 pm

Quoting Pihero (Reply 12):
The use of the landing gear was a 741 / 2 / 3 SOP, the captain had a choice of whether use them or not. It allowed a slower IAS / Mach, limited to Vle .
The procedure was awkward as it involved all three flight deck personnel being rather busy. It was cancelled on the 744 on some airlines.

Having trained both ways in the classic, I can tell you that if you from most altitudes, gear down gets you down to 14000 feet faster, and with a steeper gradient. However there are some circumstances where the steepest possible gradient is not desirable. If there is no significant structural damage (and this is a heavily debated point) you may want to get maximum mileage from your emergency descent, such as during a depressurization at or near ETP. In other circumstances, such as a cargo fire near suitable airports, you will want minimum time in the descent and minimize the stress on the airframe.

The reason structural damage is heavily debated in a depressurization scenario is that some believe that a sudden loss of cabin pressure implies some level of damage, otherwise you wouldn't have depressurized. The counter is that, the level of damage needed to depressurize the aircraft does not necessarily rise to the level of damage that would threaten the integrity of the aircraft.

The only other factor I haven't seen mentioned is high terrain. When operating over mountainous areas you may have to slow your descent while navigating an escape route.
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Pihero
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RE: How Are Emergency Descents Conducted?

Thu Mar 17, 2011 9:58 pm

Quoting lowrider (Reply 26):

The only other factor I haven't seen mentioned is high terrain. When operating over mountainous areas you may have to slow your descent while navigating an escape route.

Yes we're no longer in an emergency descent situation. The oxygen requirements become one of the limiting factors, along with a published escape trajectory.
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lowrider
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RE: How Are Emergency Descents Conducted?

Thu Mar 17, 2011 11:42 pm

Quoting Pihero (Reply 27):
along with a published escape trajectory.

Does your company provide these? We are left to our own devices for this.
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Pihero
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RE: How Are Emergency Descents Conducted?

Thu Mar 17, 2011 11:57 pm

Yes.
The documents are called "Aid to decision in case of pressurisation failure" and "Oxygen accessibility zones"Sometimes they are quite specific as the O2 equipments differ from fleet to fleet and sometimes within a fleet (22 min chemical O2 or gazeous O2, as the manufacturers can change this kind of specs.).
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Crosswind
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RE: How Are Emergency Descents Conducted?

Fri Mar 18, 2011 1:51 am

My aircraft memory items as follows;

- Continuous Ignition - ON
- Throttles - CLOSED
- Speed Brakes - DEPLOY
- Pitch - INITIALLY 20 DEGREES NOSE DOWN
- Checklist

Assuming memory items for condition causing emergency descent (eg Depressurisation) already complete.

At high altitude the IAS may well allow you to drop the gear, but it's usually not procedure - it's not required, and the speedbrakes aren't speed limited not (below VMO/MMO) on my a/c anyway.

If you're in an area of high MSA, where escape routes, or oxygen remaining become considerations, then this is normally briefed before entering that area so that everyone is agreed that if anything happens before a time/waypoint we turn back out of that area, after that point we continue, turn left/right etc. For most operations these decisions are outlined in advance as part of the route/area brief. For many operations it's a straightforward decision, eg crossing the Alps in Europe, more complex over more extensive terrain such as the Himalayas where which way to turn may require some guidance.

Oxygen is interestingly usually the most critical scenario in ETOPS operations over water;

ETOPS fuelling is the most limiting of several scenarios at an ETP. An engine failure will require the aircraft to descend to a medim level (FL250 or so) to continue to an alternate on one engine, a depressurisation will require the same aircraft to descend to FL100 to continue to an alternate at FL100 with 2 engines running (and possibly anti-ice on) Guess which one is usually limiting for critical fuel when the alternate may be 3 hours+ away?!

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474218
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RE: How Are Emergency Descents Conducted?

Fri Mar 18, 2011 2:05 am

Quoting Crosswind (Reply 30):
and the speed brakes aren't speed limited not (below VMO/MMO) on my a/c anyway.


Most aircraft spoilers have a "blow down speed". Deploying the spoilers above the "blow down speed" will result in less then full spoiler travel and as the speed is scrubbed off the spoiler will deploy further!.
 
tdscanuck
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RE: How Are Emergency Descents Conducted?

Fri Mar 18, 2011 4:23 am

Quoting Speedbird741 (Reply 25):
Quoting tdscanuck (Reply 22):
the AFM limitation is actually coded into the flap actuation logic, so if you move the handle above 20,000' nothing happens.

They would extend in the alternate flap mode correct?

I think so, but I haven't actually tried that. Good question, more research required.

Tom.
 
vikkyvik
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RE: How Are Emergency Descents Conducted?

Fri Mar 18, 2011 4:18 pm

Quoting Crosswind (Reply 30):

ETOPS fuelling is the most limiting of several scenarios at an ETP. An engine failure will require the aircraft to descend to a medim level (FL250 or so) to continue to an alternate on one engine, a depressurisation will require the same aircraft to descend to FL100 to continue to an alternate at FL100 with 2 engines running (and possibly anti-ice on) Guess which one is usually limiting for critical fuel when the alternate may be 3 hours+ away?!

Is a depressurization + engine failure considered too unlikely a situation? What would you do if that happened?
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glen
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RE: How Are Emergency Descents Conducted?

Sat Mar 19, 2011 1:23 am

Quoting vikkyvik (Reply 33):
Is a depressurization + engine failure considered too unlikely a situation? What would you do if that happened?


The simultaneous failure of one engine and loss of pressurization is also calculated on the ETOPS-analysis and is normally the most restricting scenario.
On a 4-eng aircraft in the EROPS-analysis 1-eng out, 2-eng out and loss of pressurization are calculated but not the combination of engine failure and decompression.
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AJ
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RE: How Are Emergency Descents Conducted?

Sat Mar 19, 2011 2:57 am

Quoting lowrider (Reply 26):
The reason structural damage is heavily debated in a depressurization scenario is that some believe that a sudden loss of cabin pressure implies some level of damage, otherwise you wouldn't have depressurized. The counter is that, the level of damage needed to depressurize the aircraft does not necessarily rise to the level of damage that would threaten the integrity of the aircraft.

My biggest concern would be damage to the airframe that would prohibit retracting the gear again. A bit of a problem mid-Pacific!
 
 
AJ
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RE: How Are Emergency Descents Conducted?

Sun Apr 03, 2011 9:56 pm

Quoting Chamonix (Reply 36):
77W emergency
http://videos.tf1.fr/infos/2011/atte....html

Looked more like a 772 to me.

I don't get the connection to a depressurisation. This story is about a pilot's incapacitation?
 
Pihero
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RE: How Are Emergency Descents Conducted?

Tue Apr 05, 2011 10:24 am

Quoting AJ (Reply 37):

I don't get the connection to a depressurisation. This story is about a pilot's incapacitation?

Yes, but you'll have to get used to chamonix's unique way of going all over the place to get answers !
   
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