Question Concerning Aircraft Doors

[Torontoworker]

I gather it is almost impossible to open an airliner door during flight due to several reasons, chiefly the internal air pressure (8psi?) and the doors inward then outward operation. In discussions elsewhere (other sites) concerning people attempting to open doors in flight, I recall being told by someone that once the gear has cleared the ground that a signal is sent to each door that arms a latch in the door preventing the manual arm from being used and that the cabin crew can override this and or the crew up at the pointy end of things. :) Is this true or urban myth?

[Bullethead]

"I recall being told by someone that once the gear has cleared the ground that a signal is sent to each door that arms a latch in the door preventing the manual arm from being used and that the cabin crew can override this and or the crew up at the pointy end of things.

Not on the several Boeings I've flown, can't comment about the other brands.

As you say, in a pressurised aeroplane the differential/internal pressure is about 8psi, it's actually around 9psi, that's just over 1/2 a ton per square foot. A B747 main deck door is approximately 6 feet by 3 feet so there is roughly 9 tons of force holdng the door shut when the aeroplane is pressurised. Neither you nor Superman is going to move it inflight unless the aeroplane is depressurised first.

Once the gear leaves the ground a signal is sent to the pressurisation system to pressurise the aeroplane, if it was pressurised on the ground it would be impossible to carry out a ground evacuation if necessary. When the aeroplane lands another signal is sent to the pressurisation system to de-pressurise it so that the doors can be opened.

There is no extra latching system for the doors and therefore no override function.

Regards,
BH.

[BelArgUSA]

Hola Torontoworker -
xxx
The explanation given by our friend Bullethead is quite clear and correct, although his numbers are very inaccurate. In reality the pressure exercised against the passenger main doors of a 747 is much higher than the figures he uses.
xxx
First, the 747 is NOT pressurized on the ground, as most airplanes that I know. The only exception were a slight differential pressure possible on the 707/727 types, but permitting doors to be open. So except while on the ground, and when differential is still low, immediately after takeoff or about to land, would preclude a passenger door to be opened by an idiot.
xxx
I recall once, an illustrious new flight engineer having selected "sea level pressure" with our 707 landing in Denver (5,300 feet above sea level). Upon arrival at the gate, our cabin attendants were unable to open the L-1 door... because of pressure differential... oooooops...!
xxx
Your question was often asked by newly hired flight attendants, and I often was one of the designated "sky god pilots" to brief them about some technicalities of airplanes. So I did measure the exact surface of the door (height by width) and applied the cruise pressure differential of a 747 which is normally selected at 8.5 psi by the flight engineer, that equates to 16 metric tonnes of pressure applied against the door. Even that the handle is 50+ cm long, I doubt that the "idiot" would have the muscles and leverage to counter that pressure. The pressure against a smaller door, call it a 737/757 main door, is probably around 8 tonnes, and overwing exits on a 737 probably get 2 or 3 tonnes of pressure precluding their opening.
xxx
The "manual/auto" selectors for each 747 doors only select the proper deployment of the door evacuation slides. It does not affect the opening/closing of the doors. So the "idiot" can play with that toy as long as he wishes...
xxx
No matter how "automatic" new airplanes designed for "geeks" and "nerds" will become, nobody of sound aviation mind (except Airboos maybe) would ever approve of a system locking all doors by the airplane liftoff from the runway. If "something is automatic", it "will malfunction" at the worst time requiring an evacuation.
xxx
:ok:
Happy contrails

[Flight Detent]

Thanks Guys for all your info...

Can I just fine-tune some of the points:


* True, the 747 is not pressurized on the ground, but is signalled by the weight-on-wheels switching systems to start the outflow control valves closing on liftoff. That's why, in a no-packs takeoff, the first aircon pack must be selected on prior to the outflow valves getting fully closed, otherwise you will get a good pressure bump.

* However, this is not the case with the 737NG, they start to pressurize when the thrust levers are advanced for takeoff (apparently less of a pressure 'bump' when they get it airborne), and it will depressurize if/when the thrust levers are retarded to idle whilst still on the ground.

* The entry and service doors opening handles can be moved toward the open selection, but will only result in an "Door Open" indication in the flight deck, the door, as mentioned, will not budge!

* Again, the B737NG has outward opening overwing doors, so the pressure weight on those doors is not relevent, it has other means with which to stop the doors being opened in flight.

* and yes, the B727 ground/flight switch being selected to flight (with packs operating) whilst on the ground will not stop the rear door from being opened, I've done that myself!

..just thought I'd mention those in passing...feel free to pounce on me!

Cheers...FD...:ok:

[BelArgUSA]

Hola Flight Detent...
xxx
About the 727, are you one of D.B. Cooper buddies...?
Have you jumped with a bunch of $$$ bags (worse - Zimbabwe currency...?)
In all honesty, always wondered about that little aerodynamic "Cooper" vane.
Would it be able to counter 3000 psi of hydraulics...?
Looks flimsy to me.
xxx
You know, sometimes I worry about all the technical knowledge we publish here.
These idiots who want to open door (because too hot) in flight take notes on Pprune.
How to be mischievous and make paranoia of terrorism in the news media.
Let them play with door handles, and give them vitamins to exercise.
If the smoking section is on the wing, let them go and "puff one"...
Have you got ashtrays on the leading edge of the 737NG...?
xxx
Oh well, rocking my retired pilot chair...
:}
Happy contrails

[Conan The Barber]

As is often the case there is no definite answer - despite what some think - .

It depends, as they say, on the door design and location. On the 737NG the overwing door is locked under certain conditions, as is the upper deck door on the 747-300/400.

The load on the door is a separete issue, so is the leverage you get from the handle/gearing unit in the door.

Most pilots have no knowledge of this. Neither do they know whether their pax doors are plug-type doors, semi plug-type or non plug-type doors.

[rogerg]

Most pilots have no knowledge of this. Neither do they know whether their pax doors are plug-type doors, semi plug-type or non plug-type doors

The tech part of the type rating will give the pilot this information, whether they will remember it is a different matter. The last type rating I did, on the CRJ, did not have "plug" type doors.

[Conan The Barber]

Do you really know how the doors in your aircraft are locked and secured, rogerg?

Is it held against the sill or lugs? Is it a couple of hooks at the top?

[rogerg]

Do you really know how the doors in your aircraft are locked and secured, rogerg?

Is it held against the sill or lugs? Is it a couple of hooks at the top?

Its some years since I flew it, but I seem to remember lots of lugs which had to be checked through "windows" in the door with various "align" markings.

[TightSlot]

747-400 Upper Deck Doors have an electronic latching system linked to the gear - is that what you were asking about? If you are bored enough, and sitting near these doors, you may see a small indicator light near the top of the door frame illuminate or change color when the weight comes on and/or goes off the gear.

[Flight Detent]

I seem to remember on the -300 there was a test function of the locking system amidships overhead adjacent to those upper deck doors.
Also recall that there was a requirement to post an FA at the door for takeoff if that auto locking system didn't work (MEL), until a specific altitude was reached (for internal pressure buildup to 'lock' the door).

Ahhh...the -300, the best B747 ever!!

Cheers...FD...:)

[Torontoworker]

WOW!! What a great site this is for info. The only reason I ask is that I have flown Skyservice a few times and I am going down to Margarita Island in three weeks with them and as you know, they just recently had some fool attempt to open one of their A320B doors in mid-flight over the DR. I always knew you couldn't open the door but not the *precise* reason why. Thanks.

[wiggy]

Well just to be really accurate, or a utter nitpicker. the 747 -400 series certainly is pressurised on the ground because during the later stages of the take-off roll the Outflow valves start to partially close at ? 80kts G/S.