Are airplanes supposed to be airtight?

GoWhest

I was on one of Ryanairs 737~800 the other day. I was sitting in seat 1a, shoes off and feet out. Their was an icy cold draught coming in at the bottom of the front door. Nothing major, just a small enough one. Is this normal on an aircraft? I always thought they were airtight?

IRLConor

The cabin is at a higher pressure than the outside air. If there was a leak, the air would flow out, not in.

You were probably in a draught from an air conditioning outlet somewhere.

eatmyshorts

GoWhest wrote: »

I was on one of Ryanairs 737~800 the other day. I was sitting in seat 1a, shoes off and feet out. Their was an icy cold draught coming in at the bottom of the front door. Nothing major, just a small enough one. Is this normal on an aircraft? I always thought they were airtight?

Aircraft aren't airtight. Even with the outflow valves fully closed and the packs turned off, the cabin will still climb at about 1000 feet per minute, depending on the age and condition of the pressure hull.

Katunga

no they are not. just have to have a very low pressure loss.

Lapin

GoWhest wrote: »

I was on one of Ryanairs 737~800 the other day. I was sitting in seat 1a, shoes off and feet out. Their was an icy cold draught coming in at the bottom of the front door. Nothing major, just a small enough one. Is this normal on an aircraft? I always thought they were airtight?

The Daily Mail might give you a little cheque if you go to them with that story. Just don't let on it was 'nothing major'. Use words like 'panic', 'fear' & 'prayed' and throw in a sentence about never seeing your family alive again.

They might even throw an extra few bob your way if you agree to pose for photographs with traumatised and angry expressions on your face. Preferably if the photo is taken at the perimeter fence of an airport with a Ryanair plane in the background.

ProfessorPlum

To be fair to the OP, door seals leak, and some can be very leaky. While there might not have been an icy cold draught coming in, there very probably was nice warm air going out, leaving the area feeling cold. On EI's old 747's, the seals were quite leaky and the CC used put towels on the floor around them to keep the heat in. They'd be iced up before very long.

Stevek101

I thought there was a cool draft coming from the emergency exit door on a Ryanair 738 before. After some investigated I noticed a screw/bolt along with a washer which appeared to be the source of the coldness. I always wondered since what the bolts are for, even the newest aircraft feature this modification.

pclancy

I have experienced this on many flights where I thought I was lucky getting an emergency exit seat. After 11 hours freezing I decided not to sit near exit doors ever again. I wouldn't describe it as a draft as such, just obviously much colder then the rest of the cabin.

There have been a couple of events involving Emirates and Singapore A380s recently with door seal issues and even one panel blowing out, so I wouldn't be so quick to think leaky door seals are something that doesn't happen.

Irish Steve

Can I point out the fundamental flaw in some of these posts.

Due to the fundamental requirement to keep people alive, on pressurised aircraft, (anything flying above 10,000 Ft) the pressure INSIDE the cabin is higher than the pressure OUTSIDE once the aircraft takes off. So, any leakage is from the inside to the outside.

If there's a cold draught coming from somewhere inside the aircraft, it's coming from the engine bleeds, via the pressurisation system, and the most likely cause of that is the temperature regulation of the system has been set low. When in the air, there is no way for air to be coming in to the cabin from the outside other than via the pressurisation/air conditioning route, it's just not possible.

Delta Kilo

Its quite common, regardless of the science behind how it happens. There is a mod for the A330 (not sure if its just the older vintage A330s) which installs heated panels in the floor just inside the entry and service doors to minimise the effect of this. I believe it was brought in because cabin crew were complaining of cold legs!

A330 has a notoriously leaky door.

bbbaldy

Leaky door seals are not unusual, that was the noise you heard,
Entry doors are not as well insulated as the fuselage, that was the cold you felt.
Air was not coming in from outside, had to be the other way around.
Some aircraft have supplementary area heaters around the door areas to counteract this. 737 does not.

dudara

Due to the pressure gradient, air will want to flow out. Due to the temperature gradient, heat energy will want to flow out. The transfer of heat energy may be more concentrated at the doors, (perhaps not as much surrounding insulation as you have in the cabin) and hence it feels colder there.

ProfessorPlum

The cold air around the doors is not coming from the air conditioning.

crisco10

Just a standard mechanical engineer here with my heat transfer take!

If air is leaking out, it's lovely ambient temperature air. but as it gets closer to the outside it starts to cool, hence the OP wasn't feeling an incoming draft, but more the slightly chilled air on it's way out!

2 stroke

My take on this. I know the pressure INSIDE the cabin is higher than the pressure OUTSIDE once the aircraft takes off. So, any leakage is theoretically from the inside to the outside.
However as the plane is flying at high speed, A thin layer of outside air is compressed ahead of the plane and under the wings in particular, with a deeper "vacuum" above the wings and behind the plane. This "compressed air" flows around the plane into the "decompressed" wake behind the plane. Door and window seals are helped, by the positive presure created by this layer of air pressing into any imperfections (openings) in the surface.
I do not know the actual presure diferentials, but yes, I do think it is possible for a small air leak, at an area of air turbulance, into a presurised plane. And what worries me is that if I'm right, the air leaks in other parts of the plane may be greater than what might be calculated by inflow readings.