New style emergency exits

After spending about 10 hour in the exit rows of aluminum tubes over the
last week I noticed something new. They 737-800 has a different design
than the older style overwing hatches. This is more door like. It has
hinges and opens outward. You no longer have to bring the door in and
throw it out of the hole you just created.

Two thoughts: First: for purposes of getting out of the airplane this is
better. If you have people piled up behind you getting the hatch into
the airplane would be more difficult. Problem solved.

Second: What is keeping a nut from trying to open the door in flight?
How does this system work? Do they have an evacuate button in the
cockpit that releases any locks on the overwing exit? Ok so what powers
it if you loose all generating capacity? or is there a pressure
sensitive lock on the door?

Just wondering.....
Michelle

I have to admit I would feel a bit more uneasy sitting next to an
outword opening door. Are you sure the door doesn't pull in and then
open out like the main door? Doors that open straight out require more
complex locking mechanisms because they naturally always want to open
in flight. The inward opening doors are referred to as "plug" doors
because you cannot physically open them when the aicraft is under
pressure, the air pressure holds the door firmly closed. Normally, you
only see outward opening doors for cargo where getting the door to
swing in might be difficult. In those cases there is a very complex
mechanism of cams and locks to hold the door closed against the
pressure. They are also notorious for having small leaks (not a safety
issue, just irritating).

-Robert

Robert M. Gary wrote:
I have to admit I would feel a bit more uneasy sitting next to an
outword opening door. Are you sure the door doesn't pull in and then
open out like the main door? Doors that open straight out require more
complex locking mechanisms because they naturally always want to open
in flight. The inward opening doors are referred to as "plug" doors
because you cannot physically open them when the aicraft is under
pressure, the air pressure holds the door firmly closed. Normally, you
only see outward opening doors for cargo where getting the door to
swing in might be difficult. In those cases there is a very complex
mechanism of cams and locks to hold the door closed against the
pressure. They are also notorious for having small leaks (not a safety
issue, just irritating).

-Robert

Robert,
The pictures clearly indicate: pull the handle and the door swings out
and up.
Michelle

Regardless of the motion of the door in opening, you can count in there
being pressure sensors that block the locking mechanism from actuating
when the pressure in the cabin is higher than external pressure...
They don't all have to be electrical to still be safe in case of total
electrical failure... A simple bellows mechanism, no different from
your altimeter, can push a locking pin into the doors hardware anytime
the inside pressure exceeds the external pressure...

denny

Denny wrote:
Regardless of the motion of the door in opening, you can count in there
being pressure sensors that block the locking mechanism from actuating
when the pressure in the cabin is higher than external pressure...
They don't all have to be electrical to still be safe in case of total
electrical failure... A simple bellows mechanism, no different from
your altimeter, can push a locking pin into the doors hardware anytime
the inside pressure exceeds the external pressure...

There must be some kind of override to this. Imagine the situation of
a plane sitting on the ground with a fire in the cabin. I would
imagine that would make the inside pressure higher than the outside
pressure, but clearly not a case where you want to prevent the doors
from opening.

Roy Smith wrote:
Denny wrote:

Regardless of the motion of the door in opening, you can count in there
being pressure sensors that block the locking mechanism from actuating
when the pressure in the cabin is higher than external pressure...
They don't all have to be electrical to still be safe in case of total
electrical failure... A simple bellows mechanism, no different from
your altimeter, can push a locking pin into the doors hardware anytime
the inside pressure exceeds the external pressure...


There must be some kind of override to this. Imagine the situation of
a plane sitting on the ground with a fire in the cabin. I would
imagine that would make the inside pressure higher than the outside
pressure, but clearly not a case where you want to prevent the doors
from opening.

I know that our airline evac checklist includes the pushing of the
emergency depress. Otherwise the main door will not open. Had to test it
a few times and it is kinda fun....
The more I thought about it a simple differential pressure switch that
dis-engages the handle would work nicely.

Michelle

Michelle wrote:
After spending about 10 hour in the exit rows of aluminum tubes over the
last week I noticed something new. They 737-800 has a different design
than the older style overwing hatches. This is more door like. It has
hinges and opens outward. You no longer have to bring the door in and
throw it out of the hole you just created.

Two thoughts: First: for purposes of getting out of the airplane this is
better. If you have people piled up behind you getting the hatch into
the airplane would be more difficult. Problem solved.

Second: What is keeping a nut from trying to open the door in flight?
How does this system work? Do they have an evacuate button in the
cockpit that releases any locks on the overwing exit? Ok so what powers
it if you loose all generating capacity? or is there a pressure
sensitive lock on the door?

Just wondering.....
Michelle

You are correct. When I worked at Boeing, I did an evac drill through a
mock up of these doors. When the lever is pulled, the door swings out
and up above the aircraft. No need to pull the plug door into the cabin.

If I recall correctly the -800 and -900 have 4 of these doors.

I'm not sure how they are set up to prevent a nut from popping the door.
I can think of two possible engineering solutions that may be involved.

The first would be some sort of small deflector that uses the airflow
across the door to create enough pressure to prevent it from being
opened while the aircraft is moving.

The other would be a solenoid lock that can be enabled/disabled.
Solenoids have a failure mode, so if there was a loss of electricity, it
would be enabled.

There probably is something more elegant than those solutions-

Len

"Roy Smith" wrote in message ...

... Imagine the situation of
a plane sitting on the ground with a fire in the cabin. I would
imagine that would make the inside pressure higher than the outside
pressure, ....


Have you ever seen the trick to get a hard boiled egg into a pop bottle. Put a smoldering piece of paper in there then
put the (shelled) egg over the bottle opening. The burning paper consumes the O² in the bottle and the egg gets pulled
inside....