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Cabin Pressurisation Affecting Evacuations With Do

Mon Oct 16, 2000 3:41 am

If I remember correctly, quite a few years ago a Saudi L10-11 came in for an emergency landing, and everyone onboard died because the captain was overcome by smoke before he could shut down the engines and equalise the air pressure. This prevented the cabin crew from opening the doors, even though they managed to start the evacuation. Is this correct, and how does it affect evac procedures if, for example, the engines shut down, or are torn from the aircraft on impact, but the main cabin stays pressurised?

RE: Cabin Pressurisation Affecting Evacuations With Do

Mon Oct 16, 2000 6:09 am

It's pretty unlikely that the cabin would remain pressurized. The landing gear are equiped with squat switches which, among other things, send a signal to the pressurization controller which opens the outflow valve, allowing air to escape from the cabin. Thus the cabin depressurizes.

What if the gear aren't down, you ask? Well, assuming for the moment that the pressure vessel has in no way been compromised (a pretty big assumtion), than all aircraft doors and exits are equiped with various ways of gradually relieving pressure during the opening sequence in order to prevent injury to the operator of the door mechanism(s).

Hope that answers your question.
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RE: Cabin Pressurisation Affecting Evacuations With Do

Mon Oct 16, 2000 6:40 am

However, apparently not all aircraft have the squat switch/pressure relief feature.

FedEx flight 1406, a DC-10 was forced to make an emergeny landing due to a smoke warning. During the evacuation on the ground, the flight engineer was unable to open the door. He then manually opened the outflow valves and the crew escaped the ensuing fire. Incidentally, the Capt. and F/O escaped down ropes through the cockpit windows.

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RE: Cabin Pressurisation Affecting Evacuations With Do

Mon Oct 16, 2000 8:02 am

It's interesting you mentioned this accident because it was used as an example of what not to do as a crew in one of the Crew Resource Management (CRM) courses I took a few years back.

In that class, nothing was mentioned about the pressurization that prevented evacuation. I don't think it was a factor. In that class, we got to read the the transcript of CVR and it was a little bit strange and painted an entirely different picture on this one.

The crew consisted of two Saudi and one American. The Cpt and FO were Saudi with the American as a flight engineer (FE). Shortly after takeoff, the instruments detected a fire in the back. The Cpt asked the FE to re-check the instruments and the FE kept saying there was no fire. Several long minutes went by with the FE refusing to accept there was any fire. The Cpt then asked the FE to go back and check and several minutes later the FE came back with a negative. As recorded on the CVR, the Cpt told the FO in Arabic that the FE was a jackass and decided correctly to turn back to land anyway. They landed back at the origin airport without mishap. At this point there was shouting in the back that smoke was seen. However the Cpt never gave the order to evacuate. Nobody knew why but speculations were abound that the Capt was trying to clear the runway before ordering to evacuate because the Saudi King's plane happened to be taxiing for takeoff (or landing, I couldn't recall). The crew apparently died of smoke before they could order evacuation. Everybody onboard perished as a result. The firetrucks were there also but never did anything either until it was too late.

Interesting, later, they found through records that the American FE was dyslexic and when under stress could not read the instruments correctly, thus the reasons for repeated denials, costing many precious minutes. The FO was highly inexperienced and therefore never asserted himself. The Capt made the correct call to come back but failed to order evacuation out of respect for the King.

Best Regards,
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RE: Cabin Pressurisation Affecting Evacuations With Do

Mon Oct 16, 2000 11:58 am

I think you may have this combined with another accident. Although this one could qualify as an example for CRM training as the outflow valves were supposed to have been opened during an emergency procedures checklist, were said to be opened, but obviously weren't if the cabin was still pressurized on the ground.

Additionally, the FE repeatedly asked the pilots for the airport's three-letter identifier, was told, but asked again later. And ultimately, was unable to find the approach on his laptop.

You're right, the ARFF teams were unable to get into the plane at first and then hesitant to enter or pierce the skin of the A/C.

Unfortuantely, the NTSB summary isn't very descriptive:

RE: Cabin Pressurisation Affecting Evacuations With Do

Mon Oct 16, 2000 10:26 pm

MD-11 Nut and Minuteman,
Hello;A few items to complete your posts:
-The captain took more than 25 minutes after the first report of fire by the purser to make the decision to return to Riyadh.
The pressurisation logic has already taken the cabin altitude down in preparation for a landing at Jeddah which is at sea-level instead of the 4500+ ft of Riyadh.
-The descent and approach check-lists were never completed due to a total break of cockpit coordination.
-The fire destroyed the electrical control to the outflow valves,preventing the AIr/Groungd logic to fully open them at touch-down.
-There was no preparation for any sort of emergency from the captain in spite of repeated calls from the cabin crew who then had to deal with a full-blown cabin fire and panicking passengers.
-The captain ended his performance with a kiss landing and an exit of the runway at the farthest TWY;the report on a royal plane has never been confirmed.
-The captain's last words were "We're going to evacuate" after being alerted of the seriousness of his situation by the tower.
By then it was too late.The entire aircraft above the floor was destroyed by the flames.
Very sobering,isn't it?
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RE: Cabin Pressurisation Affecting Evacuations With Do

Tue Oct 17, 2000 4:17 am

Additionally the F/E was dyslexic and was unable to read the Chk lists properly.

After landing the F/E triggered the Oxygen system so once that O2 got out that was it.

When rescue services got on to what was left of the a/c the cockpit was full of bodies as people rushed forward to escape the smoke prior to the O2 flashover.
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RE: Cabin Pressurisation Affecting Evacuations With Do

Thu Oct 19, 2000 1:31 am

A couple of years back a third world A340 operator turned up at LHR where there was a delay in opening the pax door. While we were wondering what was wrong, the Capt opened the DV window and shouted down that there was a problem with the pressurisation system and the a/c hadn't depressurised .....................Think about it.

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