You would be right, if the doors on pressurised aircraft opened that way. But they don’t - you can only open them by pulling them into the cabin. Which is only possible when the cabin is unpressurised. However, my follow-up question for those more knowledgeable is: what about at low altitudes - is it possible then that the pressure differential between outside and inside the cabin is insufficient as a safeguard against this? Or is it the case that shortly after the cabin doors are shut in preparation for take-off, the cabin is pressurised to a high enough degree compared with the outside that it quickly becomes impossible to open the doors, before takeoff?
I asked a question a few years ago, as to how many pounds of pressure are on a typical passenger jet door when the aircraft is pressurised. That is, how much does the door ‘weigh’ – how much would you have to ‘lift’ – to overcome the pressure and pull the door in.
How big is the door?
It looks like it is about 2 ft by 4 ft, which is 8 square feet. At 144 square inches in a square foot, that works out to about half a ton per psi of pressure differential. That adds up to unliftable by a human pretty quickly.
The pressure difference between 35k feet (common cruising altitude) and 6000 feet (common internal pressure equivalent) is about 8 psi. A normal passenger door is about 42x72 in, for 24,000 lbs, or 12 tons. Good luck with that.
I was just doing a back of the envelope calculation. Thanks for the more accurate information.
Sure thing; I didn’t really mean that as a correction, just extra info. Some doors are likely smaller, like the emergency exits. Either way, there’s no way you’re getting one of those doors open at altitude.
Also, a small correction: most airliners are pressurized to 8000 feet. The 787 and a few other new planes are pressurized to 6000 feet, though.
Others have addressed the cruise situation. Though it’s not quite as simple as lifting 24,000# because the door handle operates some cams with a lot of mechanical advantage to “crack” the door off the seals. So It would take far less than 24,000# of torque on that 2-1/2 foot handle to break the seal and begin to leak pressure out. Widebody aircraft may have electric motors or similar to help the door open. But all those helpers are deactivated once airborne. No matter the details, it’d be a superhuman effort.
Speaking about airliners in general, not any specific make/model …
The pressure differential is typically maintained at a very slight positive level during taxi and takeoff. Enough to prevent the doors from rattling and rain leaking in. But not enough to impede an evacuation following an aborted takeoff. As well, dumping any/all residual pressure is part of the standard management process for an evacuation.
We land similarly, with a very slight positive pressure on the aircraft which is automatically released upon touchdown so any post-landing evacuation is unimpeded. Taxi-in maintains the same very slight positive pressure as taxi-out.
As others have said, most cabin & galley doors open first inwards, then rotate to fit out the opening and stow outside the cabin when open. So the positive cabin pressure locks them closed. Conversely, many of the over-wing exits open outward. Those generally include a separate mechanical interlock arrangement connected to the airplane’s logic so the doors are unopenable during a takeoff, flight, or landing, but would be during taxi, during / following an aborted takeoff, or following a landing or post-landing mishap.
As you may have seen on the news or YouTube, once in awhile a crazy person opens an over-wing exit during taxi & jumps out on the wing. That’s as designed, since the airplane can’t tell a crazy person from an excellent decision to leave the airplane to escape a fire or ???. But you’ve never seen, and won’t see, a story of somebody getting out there during a takeoff or landing.
You raise a valid point that during low altitude flight in the, say, 1-5 minutes post-takeoff or pre-landing the differential pressure is real low and perhaps a determined strong person could get a door cracked open. But there’s no way they’re going to muster the muscle to swing that door outwards and forwards against 150-250 knots of wind outside. You’ll notice in all cases the door path wither swings out and forwards or slides out parallel to the fuselage then translates forwards. That’s to ensure they can’t be opened and will tend to blow closed if somehow they do get a bit open in flight.
The folks that design this stuff have it pretty well under control.
Excellent local knowledge throughout your post. Thanks for sharing. You also explained something that had given me pause. Namely how the captain who’d presumably been flying in and out of HNL for years wasn’t aware of the trap at taxiway K. The answer is that big jets rarely, bordering on never, use it. Until airport construction changed the operating techniques.
As to taxiway K and your snip I quoted above, while there is space in the crotch between the runways for at least a small airplane to physically be between the runway edges, it’s regulatorily impossible. The position of the hold-short lines is such that there is no legal space outside of one runway that’s not already inside of the other runway.
As specifically applicable to the UAL exiting 4R, by the time the very tip of the nose is across the line to exit 4R that same nose is already impinging on the legal boundaries of 4L and 8R. While meanwhile 200 feet and 100 tons of jet are still obstructing on 4R.
You can still back taxi on the crossover runways if someone falls into the K-trap. Might have to wait your turn but it shouldn’t stop the rotation of the planet.
Just in case it’s of interest to any casual readers following along here, although the AF447 accident has been discussed endlessly, and many of us have even read the interim and final reports, I was not aware that Petter Hörnfeldt – the creator of the well-regarded “Mentour Pilot” series of videos – had done a nearly hour-long video on it. It’s informative even for those who know many of the basic facts, but should be of particular interest to those who don’t. Petter always does a fantastic job of analysis and exposition:
Breaking News! Reno Air Races to Sunset after this year!
Just heard this on the local news… After over 60 years, they are packing it up. Unclear if it’s moving or over. Bummer! This event has always been part of my life. Went with my dad as a kid, took my kid for many years and lately been going out with my Dog Crew. Had a ‘private spot’ I’ve been hitting for over 20 years running. Always enjoyed the Unlimited Class. I’ll miss going…
Also on the same news broadcast, coverage of the funeral of the crew of the crashed Carefight a few days ago.
This from an Aussie news site about an event involving a USA carrier in Havana. Offered here without comment:
Proving once again that dogs are way, way smarter than people! In the face of one of the biggest emergencies ever, Roselle got herself and her human charge the hell out of the situation, fast. Maybe airlines should carry dogs to show idiot humans what to do in an emergency.
The dogs would also be useful when passengers decide to engage in fistfights by biting them on the ass.
I think you misspelled “neck” there at the end. Otherwise two thumbs up!
In somber news:
No NTSB prelim on this one yet. The SF50 is fully in production, so the loss of this guy is unlikely to kill the program. But it’ll be a challenge for such a relatively small company to deal with.
As they say, when autopilot is perfected, the cockpit will only have a pilot and a dog. The pilot is there to feed the dog, and the dog is there to bite the pilot if they touch the controls. I think we can use the same dog!
Damn. it’s 5 miles to the river so you would think he had some altitude to work with. I wonder if it was a medical situation.
It’ll be interesting to find out if his plane had a 'chute installed (the CAPS system), and whether it would have been relevant.
Sometimes I think the safety briefing should be a bit more hard hitting.
“If evacuating the aircraft, leave all bags behind otherwise people will burn and die. If they aren’t going to burn and die, neither will your bags so still leave them behind”.
Aren’t flight attendants trained to push passengers out the door if they hesitate during an evacuation? Granted, that’s not possible if they’re out the door and standing on the wing.
I don’t want to defend the selfie-takers on the wing, but I can at least understand why they’re still up there.
The 737 is unique in that it has slides for the fore and aft doors, but no slides for the overwings. The pilots are supposed to lower the flaps fully, and evacuees are supposed to slide down the flaps. As they’re less than 6 feet off the ground, no slides are required. There are arrows on the wing pointing you aft when you come out of the overwing exit - to this odd cliff that really doesn’t looks like its part of the evac route. Very non-intuitive.
I’ve been on a fair number of '37 wings, and only slid down the flaps once (the mechanic from US Air said it was okay and we wouldn’t damage anything). It was far from a comfortable ride, and I would not recommend it unless you’ve got a fire chasing you out of the aircraft.