Q For Enginners. Doorways; Are They Reinforced?

[steve181]

The title is vague so I'll expand on it. The fuselage area just underneath the four main door's on the 737-300 for example, I assume they are particularly robust given air bridges, stairs, catering, cleaning trucks etc regularly dock with that fuselage area.

My question is how strong is this area? How hard would an air bridge for example have to impact on that area to ground the aircraft? Could it deal with one ton of pressure for example?

Thanks.

[mainwheel]

Steve,

Any opening in a pressurised fuslage requires the cutout area to be strengthened for obvious reasons.

To answer your question quantitivly regarding 1 ton of force, you would have to know the surface area of the fuselage being touched by the force.

The fuselage is built to stand an pressure of approximately 8.5 Pounds per square inch.

Do the math.

The fuselage can also move sideways when struck.:confused:

[Storminnorm]

Areas around the doors are usually reinforced to some degree
to allow for some impact damage.
It's not unknown for airstairs or catering vehicles to cause such
damage to the aircraft structure, but thankfully these are very
rare events, and most equipment operators are very aware of
the consequences of their actions.
In my entire time in the industry I can only recall a few occasions
when an aircraft has had to be withdrawn from service as a result
of this sort of thing happening. Mainly because I was quite often
the bloke that had to repair the damage, and had a habit of venting
my spleen on whoever caused it.

[lomapaseo]

In general (not a complete answer for point impacts) a pressurized fuelage is much happier if it deflects as smoothly as a baloon. So if you start cutting holes in it you are going to have to add material to force the fuselage not to kink around those big holes. This typically adds stiffness against inward buckling as well.

Take a gander at crashed planes in the R&N threads and you will see that the door locations are the last to buckle and break the fuselage.

For point impacts, the fuselage skin is the defence and that tends to be similar thickness over the pressurized areas.

[GS John]

Have a look at how many high usage aircraft that use steps on the rear have repairs in the area ;) And repairs on the repairs :{ Can't over strengthen it as has been said as then that'll be the stress raiser and where the "strengthening" will be self defeating.
Add in that's usually where the galleys / toilets are, and it's the area you really don't want bashed.

[Parapunter]

As an aside, I was once repsonsible for a fleet of airline catering trucks. To give a perspective from the other side as it were, we would routinely be crapping ourselves within 10ft of any aircraft - our SOP was pull up 20ft away, drivers mate jumps out & stands 2ft in front of fuselage doorway & guides truck into position at a crawl.

It would really have been the end for any member of staff who smashed up an aircraft, so we took it very seriously as everyone within the ramp boundaries should.

Didn't stop us from smashing lumps out of a compressor on the LGW south term road & knocking out the aircon in the middle of August though.:ugh: