Principle: Balloon expands. Balloon pops. Why.
Fuselage undergoes internal pressure. Door pops. Why.
Boundary layer will reduce the actual speed of the air across
the door to a very low amount. Further away from the door the
airspeed builds up. The sucking force of the jet engine is negligible.
The main force to open door comes from within. The internal pressure
against the large forward cargo door is very, very high. The door
will have to be open some distance before the slipstream can tear
it open, up, and away.
All that is needed for the door to be pulled out and torn up and
away is a lip of the door to protrude into airstream. A slight
bulge on a worn door will stick door edge out into 300 KCAS slipstream
and allow the air to pull door out and tear it away. What can
cause the door edge to stick out? How much is needed? Assuming
300 KCAS of force over the door, high internal pressure to keep
passengers comfortable, the edge of the door does not have to
stick out very far before being pushed from within, and blown
from the front. Let us assume two inches sticking out from the
bottom of the sill is the amount than once reached the forces
of wind take over and tear eight foot by nine foot door away.
What would cause bottom of door to extend out two inches?
The midspan latches have no locking sectors at all so the modification does not apply to them at all. Is it not strange that the risk of latch cams becoming unlatched, and they have several times, is so great as to warrant locking sectors yet the two side midspan latches have none? And each of them holds in more door sill than the lower latches. That is an astonishing discovery: no locking sectors on all Boeing 747 forward cargo door latches which have rupture evidence at that midspan latch as shown on UAL 811 recovered door.
The absence of locking sectors for the midspan latches and the AD to strengthen the eight locking sectors for the lower eight latch cams explains much.
It probably solves how the forward cargo door of AI 182 and TWA 800 ruptured at aft midspan latch while the bottom latches remained latched in place: that is the locking sectors did their job on those two doors and prevented the eight lower latch cams from being driven into the unlatched position when chafed wires shorted and turned door motor on. Unfortunately the midspan latches had no such protection and were driven into the unlatched position enough for the internal pressure to rupture at that now weakened area leaving similar shattered door pieces and bottom latches still attached to lower sill for AI 182 and TWA 800.
For UAL 811 and Pan Am 103, the soft, pre-AD, locking sectors were overridden by door motor and all ten latches were driven into the unlatched position allowing the door to open completely and slam upward, breaking in two and tearing away, leaving the identical pattern of torn away fuselage skin and door broken in half longitudinally at midspan latches for each door.
Four aircraft, four door motors to unlocked position, two locking
sectors held and two didn't; two partial openings/ruptures and
two total openings as reflected in the reconstructions and photographs
of wreckage. AI 182 and TWA 800 had locking sectors hold so ruptures.
PA 103 and UAL 811 had locking sectors overridden so entire door
opened and came off.
1. Pneumatic: If the air keeps on coming into the balloon and
less air escapes the balloon expands until pressure inside balloon
exceeds strength to contain pressure. Balloon pops at weakest
spot on surface.
a. If air keeps coming into Boeing 747 fuselage with less air
escaping, the fuselage will pop at weakest spot, a large door.
Or if there is a small opening in fuselage, air may escape or
air may enter from 300 KCAS airstream until door bulges out. If
a hole appears in a seal of the cargo compartment, or a hole appears
from corrosion, the 300 KCAS airstream might enter compartment
and highly pressurize to cause door to bulge out the necessary
small amount to allow a larger hole to allow more airstream to
enter and the cycle continues rapidly until door is open enough
for wind to tear it away. All the steel latches in the world are
not strong enough to withstand 300 KCAS against a large surface
door.
b. If the fuselage is balanced in pressure and the aircraft starts
to climb that balance is disrupted and the system attempts to
compensate. If the compensation is not smooth, or it is jerky,
a surge of high pressure air may momentarily bulge out the door
the required amount for it to be torn away. The puff off high
pressure air may only last for a seconds before the pressurization
system corrects its balance but that may be long enough to open
a worn door with gouged latch cams and lock sectors. So, if there
is a malfunction in pressure regulating devices of 747 then too
much air may enter and may bulge worn door out enough to be torn
away.
c. If older fuselage flexes enough the worn seal on a worn door
may leak allowing air to enter cargo compartment pressurizing
it and pushing out on door which opens more allowing more air
in to pressurize compartment which pushes out on door...
d If pilot applies power to all engines, increased air requirements
result in increased sucking power of jet intakes which may allow
cargo door to bulge toward engine number 3, just a few yards away.
Very unlikely because of 300 knot slipstream which negates any
suction of the jet engine on the door.
e. The midspan latches may be a weak area. One latch holds eight
feet of vertical side of door in tight. The door may fracture/rupture
at midspan and open. The bottom latches may remain latched. Fuselage
distortion and twisting may put unusual stresses on door frame.
f. Engine cowling comes loose. Possible sequence: EPR/EGT indication
of surge as loose cowling on number three comes off, shown as
radar blip, bleed air from three affected, more heat/air goes
into forward cargo compartment, overpressure blows out weakest
area, around or through cargo door. Nose then comes off sequence
follows as evidence shows. All suspect planes have JT9D. Cowlings
have come off many times before. Cowling would explain radar blip
too early in sequence for door. Cowling reflects light. Engine
bleed air comes from three and others and goes into forward cargo
compartment. Ducts fail. Blow out around/of door would explain
latches being latched yet door goes.
2. Electrical:
a. Door actuator motor gets signal to open and turns cams which
are normally stopped by lock sectors, but worn lock sectors allow
cams to turn just a few degrees which allow door to slightly open.
b. Frayed wires in door motor bundle rub against metal fuselage
and short connection and turn motor on for a few seconds.
c. Motor gets signal to turn on from adjacent powerful transmitters
in main equipment compartment.
d. Exhaust Pressure Ratio related problem:
800 had EPR changed before fatal flight
103 had EPR blip on #3 just before crash.
182 had EPR gripe not fixed for fatal flight.
811 could have had EPR gripe but all non cargo door gripes omitted
from report.
3. Mechanical:
a. The cam sectors are not completely over center and therefore
can be forced open by internal force.
b. The manual locking handle jams and looks locked but isn't.
c. The locking sectors get bent and do not fully engage cam sectors.
d. Something unseen is jammed between door and frame preventing
full closure.
e. Loader rams door sill and bends it out of rig preventing flush
closure.
4. Combination of factors:
a. Worn latches, not tight.
b. Worn lock sectors, not tight.
c. Not closed fully, not tight.
d. Pressure regulating system not smooth.
e. Door out of rig slightly, not tight.
f. Electrical short in door open system.
g. Must be going 296 KCAS or higher.
e. Older fuselage twisting and flexing.
f. Small hole from corrosion or worn seal allowing high speed
air in with no way out.
g. Door motor gets signal to open.
Miscellaneous:
a. It is never closed fully and pops open when pressure differential
is high enough.
b. It was backdriven manually damaging cams allowing door to spring
open.
c. It was back driven electrically damaging lock sectors.
d. Fuselage flexing normal or by turbulence allowed door to spring
open.
e. Electrical short within door opening system turning on door
actuator motor.
f. Loose heavy cargo shifts into door.
g. Internal explosive force against door.
h. Locking pins shearing and releasing door to open.
i. Intentionally/unintentionally opened by crew inflight.
j. Electrical power surge from communication radio antenna or
power supply.
k. Frayed electrical wires to door control system shorting on
fuselage.
l. Passenger using electronic device triggering door open signal.
m. At certain airspeed the wind has enough force to pry open poorly
sealed door.
n. When door closed it squeezed against something that prevented
full closure allowing later opening.
o. A ship or aircraft was pointing laser tracking device on aircraft
and it penetrated door and ignited something which blew out door.
p. Surface to air missile hits door and opens it.
q More to come...open for suggestions, can't fix it without knowing
the problem, can't stop the effect of crashing without knowing
the cause of door rupture/opening.
First AAR had wrong cause for door opening, improper latching.
Once door was found, a switch was found to be defective changing
probable cause to electrical short.
Frayed wires in door motor control bundle.
Airspeed crept up to above recommended speed, 296 knots instead
of 290 knots because of fifth engine in pod.
Older airplane, night door closing
Extremely old airplane, night door closing, running late.
The first rule in designing and building a pressurized hull
is: Don't cut holes in it. If one must cut holes in the hull for
essential reasons make sure the holes are small well sealed. And
then if the hole fails to seal, make sure the hull does not come
apart.
Those principles were violated in aircraft and submarines to the
dismay of the families of the victims of inadvertent door openings
in pressurized hulls.
The nuclear submarine Thresher was sunk because a small hole in
the hull had a valve installed backwards so the water kept on
coming in and sunk the boat and killed everyone on board.
UAL Flight 811 had a cargo door open inflight and nine passengers
were sucked out to their deaths from their seats above the cargo
door.
The design errors on doors for Boeing 747 are as follows.
1. The hole is too large. It is large to accommodate passengers'
spare clothes and other non-essential items. A small hole will
depressurize slowly and not allow huge amounts of fast moving
air into the hull.
2. The hole has a complicated door system for locking and unlocking
which is prone to misuse. In fact two Airworthiness Directives
have been issued against that specific door, the forward lower
lobe cargo door.
3. a. The door is hinged on top and opens upwards. The tradition
of passengers entering by a front hinged door and baggage loaded
into a top hinged door goes back to stagecoaches, buggies, cars,
trains, and buses. And when those cargo doors opened the penalty
was bashed baggage and damaged doors. At speeds above 200 knots
such an error has catastrophic results. The door opens and the
airstream pushes the door up and tears it off it upper hinges
taking away as large part of fuselage skin, exposing the nose
of the aircraft to huge amounts of powerful fast moving air. Top
hinged doors on fast moving pressurized hulls is a fatal design
error. They also exist to ease the loading of the non-essential
items by the baggage handlers.
b. Doors hinged on the front are slightly better but the door
will still flap around and eventually break off leaving a large
hole. The air pressure will attempt to keep the door closed. A
front hinged door, when it opens in flight, will at least give
the crew time to slow the airplane down to reduce flutter and
possibly allow safe return to land.
Cargo doors, and passenger doors, and engine doors, and access
doors will all be left open or open by themselves sooner or later.
The effect should be mild and easily corrected. The consequences
for that small oversight should not be total destruction and death.
1. Big Airplane Doors that open when they shouldn't.
Forward lower cargo door in Boeing 747 resulting in nose tearing
off and rest of airplane disintegrating into fireball. Cause of
door opening unknown.
2. Medium airplane canopy that opened when it shouldn't.
RA-5C Vigilante reconnaissance carrier jet on final approach and
rear canopy popped up and was lost at sea. Aircraft recovered
safely. Thousands of dollars lost, plane grounded until replacement,
cause unknown.
3. Small airplane doors that open when they shouldn't.
Right hand side passenger door on Beech Baron. On takeoff door
popped open. Experienced passenger held door tight to keep it
from flapping. Pilot returned and landed. Door closed and airplane
resumed flight. Two months later same plane took off with different
pilot, immediately went into steep climb, stalled, crashed, two
killed, pilot and inexperienced passenger. Cause unknown.
4. Spacecraft door that opened when it shouldn't.
Gus Grissom on a Mercury spacecraft after landing in water and
hatch popped and craft sank. Valuable scientific data lost. Cause
unknown.
5. Car door open when it shouldn't.
Rear hatchback on 1984 Honda Civic opened. Car stopped and hatchback
closed. No damage. Cause was driver error in not slamming hatch
shut.
6. Submarine valve open when it shouldn't.
USS Thresher valve installed backwards, water entered and couldn't
be stopped. Ship sank, all aboard killed. Cause installation error.
7. House door open when it shouldn't.
After evening out occupants returned home to find front door unlocked
and open. Cause negligence of home owners leaving in a rush and
door open.
8. Motorcycle saddlebag open when it shouldn't.
Kawasaki Concours sport tourer motorcycle right side saddlebag
had top two clasps only partially closed. Error noticed in mirrors,
stopped, closed clasps on saddlebag and resumed ride. No damage,
cause was rider negligence.
9. Ferry door that opened when it shouldn't.
An Estonian ferry between Tallin and Helsinki had front cargo
door open, sank ferry, high loss of life. Cause was pilot going
too fast in heavy seas. Wreck to be encased in concrete on seabed.
10. Car door that closed when it shouldn't.
1949, car door slammed on finger disfiguring tip for life. Extreme
pain. Cause miscoordination between person slamming door and person
with fingers in the way.
11. Spacecraft door that wouldn't open when it should.
Apollo 1 capsule caught on fire on ground and crew could not escape
because hatch would not open. Three killed.
12. House door that shut when it shouldn't.
Hot day and doors open to let in air and breeze came up. Air flow
started closing door which accelerated and slammed shut with loud
bang waking baby.
13. Door stayed shut and wouldn't open when they should.
Cocacabana nightclub fire, exits blocked, many died. Doors sealed
shut to prevent unauthorized entry.