Aviation Incidents and Accidents

Posted by PITHOCRATES - March 12th, 2014

Technology 101

The Pilots of Aloha Airlines Flight 243 landed Safely after Fatigue Cracks caused Part of the Cabin to Disintegrate

The de Havilland Company introduced the jet airliner to the world.  The Comet.  A 4-engine jet airliner with a pressurized cabin that could carry 36 passengers.  It could fly at 40,000 feet at speeds close to 500 mph.  Just blowing the piston-engine competition away.  Until, that is, they started breaking up in flight.  A consequence of pressuring the cabin.  The inflating and deflating of the metal cabin fatiguing the metal of the cabin.  Until fatigue cracks appeared at stress points.  Cracks that extended from the cycles of pressurizing and depressurizing the cabin.  Until the cracks extended so much that the pressure inside the cabin blew through the cracks, disintegrating the plane in flight.

Japan is a nation of islands.  Connecting these islands together are airplanes.  They use jumbo jets like buses and commuter trains.  Packing them with 500+ passengers for short hops between the islands.  Putting far more pressurization cycles on these planes than typical long-haul 747 routes.  On August 12, 1985, Japan Airlines Flight 123 left Haneda Airport, Tokyo, for a routine flight to Osaka.  Shortly after takeoff as the cabin pressurized the rear pressure bulkhead failed (due to an improper repair splice of the pressure plate using a single row of rivets instead of a double row following a tail strike that damaged it).  The rapid force of the depressurization blew out through the tail section of the aircraft.  Causing great damage of the control surfaces.  And severing the lines in all four hydraulic systems.  Leaving the plane uncontrollable.  The crew switched their transponder to the emergency code 7700 and called in to declare an emergency.  But they could do little to save the plane.  The plane flew erratically and lost altitude until it crashed into a mountain.  Killing all but 4 of the 524 aboard.

Hawaii is similar to Japan.  They both have islands they interconnect with airplanes.  Putting a lot of pressurization cycles on these planes.  On April 28, 1988, Aloha Airlines Flight 243 left Hilo Airport bound for Honolulu.  Just as the Boeing 737 leveled off at 24,000 feet there was a loud explosive sound and a loud surge of air.  The pilots were thrown back in their seats in a violent and rapid decompression.  The flightdeck door was sucked away.  Looking behind them they could see the cabin ceiling in first class was no longer there (due to fatigue cracks radiating out from rivets that caused pressurized air to blow out, taking the ceiling and walls of the first class cabin with it).  They could see only blue sky.  They put on their oxygen masks and began an emergency descent.  The first officer switched the transponder to emergency code 7700.  The roar of air was so loud the pilots could barely hear each other as they shouted to each other or used the radio.  The flight controls were operable but not normal.  They even lost one of their two engines.  But the flight crew landed safely.  With the loss of only one life.  A flight attendant that was sucked out of the aircraft during the explosive decompression.

The Fact that 185 People survived the United Airlines 232 Crash is a Testament to the Extraordinary Skill of those Pilots

On June 12, 1972, American Airlines Flight 96 left Detroit Metropolitan Airport for Buffalo after arriving from Los Angeles.  The McDonnell Douglas DC-10 took on new living passengers in Detroit.  As well as one deceased passenger in a coffin.  Which was loaded in the rear cargo hold.  As the DC-10 approached 12,000 feet there was a loud explosive sound.  Then the flightdeck door was sucked away and the pilots were thrown back in their seats in an explosive decompression.  The aft cargo door (improperly latched—its design was later revised to prevent improperly latching in the future) had blown out as the cargo hold pressurized.  As it did the rapid decompression collapsed the floor above.  Into the control cabling.  The rudder was slammed fully left.  All three throttle levels slammed closed.  The elevator control was greatly inhibited.  The plane lost a lot of its flight controls but the pilots were able to bring the plane back to Detroit.  Using asymmetric thrust of the two wing-mounted engines and ailerons to compensate for the deflected rudder.  And both pilots pulling back hard on the yoke to move the elevator.  Due to the damage the approach was fast and low.  When they landed they applied reverse thrust to slow down the fast aircraft.  At that speed, though, the deflected rudder pulled them off the runway towards the terminal buildings.  By reapplying asymmetric thrust the pilot was able to straighten the aircraft out on the grass.  As the speed declined the rudder force decreased and the pilot was able to steer the plane back on the runway.  There was no loss of life.

On July 19, 1989, United Airlines Flight 232 took off from Stapleton International Airport in Denver for Chicago.  About an hour into the flight there was a loud bang from the rear of the plane.  The aircraft shuddered.  The instruments showed that the tail-mounted engine had failed.  As the crew responded to that the second officer saw something more alarming.  Hydraulic pressure and fluid quantity in the three hydraulic systems were falling (a fan disc in the tail-mounted engine disintegrating and exploded like shrapnel from an undetected manufacturing flaw, taking out the 3 hydraulic systems).  The flight crew soon discovered that they had lost all control of the airplane.  The plane was making a slight turn when the engine failed.  And the flight control surfaces were locked in that position.  The captain reduced power on the left engine to stop the plane from turning.  The two remaining engines became the only means of control they had.  Another DC-10 pilot traveling as a passenger came forward and offered his assistance.  He knelt on the floor behind the throttle levels and adjusted them continuously to regain control of the plane.  He tried to dampen the rising and falling of the plane (moving like a ship rolling on the ocean).  As well as turn the aircraft onto a course that would take them to an emergency landing at Sioux City.  They almost made it.  Unfortunately that rolling motion tipped the left wing down just before touchdown.  It struck the ground.  And caused the plane to roll and crash.  Killing 111 of the 296 aboard.  It was a remarkable feat of flying, though.  Which couldn’t be duplicated in the simulator given the same system failures.  As flight control by engine thrust alone cannot provide reliable flight control.  The fact that 185 people survived this crash is a testament to the extraordinary skill of those pilots.

On July 17, 1996, TWA Flight 800 took off from JFK Airport bound for Rome.  About 12 minutes into the flight the crew acknowledged air traffic control (ATC) instructions to climb to 15,000 feet.  It was the last anyone heard from TWA 800.  About 38 seconds later another airplane in the sky reported seeing an explosion and a fire ball falling into the water.  About where TWA 800 was.  ATC then tried to contact TWA 800.  “TWA800, Center…TWA eight zero zero, if you can hear Center, ident…TWA800, Center…TWA800, if you can hear Center, ident…TWA800, Center.”  There was no response.  The plane was there one minute and gone the next.  There was no distress call.  Nothing.  The crash investigation determined that an air-fuel mixture in the center fuel tank was heated by air conditioner units mounted below the tank, creating a high-pressure, explosive vapor in the tank that was ignited by an electrical spark.  The explosion broke the plane apart in flight killing all 230 aboard.

The Greatest Danger in Flying Today may be Pilots Trusting their Computers more than their Piloting Skills

On December 29, 1972, Eastern Airlines Flight 401 left JFK bound for Miami.  Flight 401 was a brand new Lockheed L-1011 TriStar.  One of the new wide-body jets to enter service along with the Boeing 747 and the McDonnell Douglas DC-10.  Not only was it big but it had the latest in automatic flight control systems.  As Flight 401 turned on final approach they lowered their landing gear.  When the three landing gear are down and locked for landing there are three green indicating lights displayed on the flightdeck on the first officer’s side.  On this night there were only 2 green lights.  Indicating that the nose wheel was not down.  So they contacted ATC with their problem and proceeded to circle the airport until they resolved the problem.  ATC told them to climb to 2000 feet.  The 1st officer flew the aircraft on the course around the airport.  The captain then tried to reach the indicating light to see if it was a burnt out lamp.  Then the flight engineer got involved.  As did the first officer after turning on the automatic altitude hold control.  Then another person on the flightdeck joined in.  That indicating lamp got everyone’s full attention.  Unable to determine if the lamp was burnt out the pilot instructed the flight engineer to climb down into the avionics bay below the flightdeck to visually confirm the nose gear was down and locked.  He reported that he couldn’t see it.  So the other guy on the flightdeck joined him.  During all of this someone bumped the yoke with enough pressure to release the automatic altitude hold but no one noticed.  The airplane began a gradual descent.  When they approached the ground a ground proximity warming went off and they checked their altitude.  Their altimeters didn’t agree with the autopilot setting.  Just as they were asking each other what was going on the aircraft crashed into the everglades.  Killing 101 of the 176 on board.

On June 1, 2009, Air France Flight 447 was en route from Rio de Janeiro to Paris.  This was a fly-by-wire Airbus A330 aircraft.  With side stick controllers (i.e., joysticks) instead of the traditional wheel and yoke controls.  The A330 had sophisticated automatic flight controls.  They practically flew the plane by themselves.  With pilots spending more of their time monitoring and inputting inputs to these systems than flying.  Flight 447 flew into some turbulence.  The autopilot disengaged.  The aircraft began to roll from the turbulence.  The pilot tried to null these out but over compensated.  At the same time he pitched the nose up abruptly, slowing the airplane and causing a stall warning as the excessive angle of attack slowed the plane from 274 knots to 52 knots.  The pilot got the rolling under control but due to the excessive angle of attack the plane was gaining a lot of altitude.  The pitot tube (a speed sensing device) began to ice up, reducing the size of the opening the air entered.  Changing the airflow into the tube.  Resulting in a speed indication that they were flying faster than they actually were.  The engines were running at 100% power but the nose was pitched up so much that the plane was losing speed and altitude.  There was no accurate air speed indication.  For pilot or autopilot.  The crew failed to follow appropriate procedures for problems with airspeed indication.  And did not understand how to recognize the approach of a stall.  Despite the high speed indicated the plane was actually stalling.   Which it did.  And fell from 38,000 feet in 3 and a half minutes.  Crashing into the ocean.  Killing all 228 on board.

It takes a lot to bring an airplane down from the sky.  And when it happens it is usually the last in a chain of events.  Where each individual event in the chain could not have brought the plane down.  But when taken together they can.  Most times pilots have a chance to save the aircraft.  Especially the stick and rudder pilots.  Who gained a lot of flying experience before the advanced autopilot systems of today.  And can feel what the airplane is doing through the touch of their hand on the yoke and through the seat of their pants.  They are tuned in to the engine noise and the environment around them.  Processing continuous sensations and sounds as well as studying their instruments and the airspace in front of them.  Because they flew the airplane.  Not the computers.  Allowing them to take immediate action instead of trying to figure out what was happening with the computers.  Losing precious time when additional seconds could trigger that last event in a chain of events that ends in the loss of the aircraft.  That’s why some of the best pilots come from this stick and rudder generation.  Such as Aloha Airlines Flight 243, American Airlines Flight 96 and United Airlines Flight 232.  Sometimes the event is so sudden or so catastrophic that there is nothing a pilot can do to save the aircraft.  Such as Japan Airlines Flight 123 and TWA Flight 800.  And sometimes pilots rely so much on automated systems that they let themselves get distracted from the business of flying.  Even the best stick and rudder pilots adjusting to new technology.  Such as Eastern Airlines Flight 401.  Or pilots brought up on the new technology.  Such as Air France Flight 447.  But these events are so rare that when a plane does fall out of the sky it is big news.  Because it rarely happens.  Planes have never been safer.  Which may now be the greatest danger in flying.  A false sense of security.  Which may allow a chain of events to end in a plane falling down from the sky.  As pilots rely more and more on computers to fly our airplanes they may step in too late to fix a problem.  Or not at all.  Trusting those computers more than their piloting skills.



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Corduroy Roads, Positive Buoyancy, Negative Buoyancy, Carbon Dioxide, Crush Depth, Pressurization, Rapid Decompression and Space

Posted by PITHOCRATES - May 9th, 2012

Technology 101

Early Submarines could not Stay Submerged for Long for the Carbon Dioxide the Crew Exhaled built up to Dangerous Levels

People can pretty much walk anywhere.  As long as the ground is fairly solid beneath our feet.  Ditto for horses.  Though they tend to sink a little deeper in the softer ground than people do.  Carts are another story.  And artillery trains.  For their narrow wheels and heavy weight distributed on them tend to sink when the earthen ground is wet.  Early armies needing to move cannon and wagons through swampy areas would first build roads through these areas.  Out of trees.  Called corduroy roads.  It was a bumpy ride.  But you could pull heavy loads with small footprints through otherwise impassable areas.  As armies mechanized trucks and jeeps with fatter rubber tires replaced the narrow wheels on wagons.  Then tracked vehicles came along.  Allowing the great weights of armored vehicles with large guns to move across open fields.  The long and wide footprints of these vehicles distributing that heavy weight over a larger area.  Still, nothing can beat the modern rubber tire on a paved road for a smooth ride.  And the lower resistance between tire and road increases gas mileage.  Which is why trucks like to use as few axles on their trailers as possible.  For the more tires on the road the more friction between truck and road.  And the higher fuel consumption to overcome that friction.  Which is why we have to weigh trucks for some try to cheat by pulling heavier loads with too few axles.  When they do the high weight distributed through too few wheels will cause great stresses on the roadway.  Causing them to break and crumble apart.   

Man and machine can move freely across pretty much anything.  If we don’t carry food and water with us we could even ‘live off the land’.  But one thing we can’t do is walk or drive on water.  We have to bridge streams and rivers.  Go around lakes.  Or move onto boats.  Which can drive on water.  If they are built right.  And are buoyant.  Because if a boat weighed less than the water it displaced it floated.  Much like a pair of light-weight, spongy flip-flops made out of foam rubber.  Throw a pair into the water and they will float.  Put them on your feet and step into the deep end of a pool and you’ll sink.  Because when worn on your feet the large weight of your body distributed to the light pair of flip-flops makes those flip-flops heavier than the water they displace.  And they, along with you, sink.  Unlike a boat.  Which is lighter than the water it displaces.  As long as it is not overloaded.  Even if it’s steel.  Or concrete.  You see, the weight of the boat includes all the air inside the hull.  So a large hull filled with cargo AND air will be lighter than the water it displaces.  Which is why boats float. 

Early sail ships had great range.  As long as the wind blew.  Their range only being limited by the amount of food and fresh water they carried.  Later steam engines and diesel-electric engines had greater freedom in navigation not having to depend on the prevailing winds.  But they had the same limitations of food and water.  And when we took boats under the water we had another limitation.  Fresh air.  Early submarines could not stay submerged for long.  For underwater they could not pull air into a diesel-electric engine.  So they had to run on batteries.  Which had a limited duration.  So early subs spent most of their time on the surface.  Where they could run their diesel engines to recharge their batteries.  And open their hatches to get fresh air into the boat.  For when submerged the carbon dioxide the crew exhaled built up.  If it built up too much you could become disoriented and pass out.  And die.  If a sub is under attack staying under water for too long and the levels of carbon dioxide build up to dangerous levels a captain has little choice but to surface and surrender.  So the crew can breathe again.

Rapid Decompression at Altitude can be Catastrophic and Violent

Being in a submarine has been historically one of the more dangerous places to be in any navy (second to being on the deck of an aircraft carrier).  Just breathing on a sub had been a challenge at times while trying to evade an enemy destroyer.  But there are other risks, too.  Some things float.  And some things sink.  A submarine is somewhere in between.  It will float on the surface when it has positive buoyancy.  And sink when it has negative buoyancy.  But submarines operate in the oceans.  Which are very deep.  And the deeper you go the greater the pressure of the water.  Because the deeper you go there is more ocean above you pressing down on you.  And oceans are heavy.  If a sub goes too deep this pressure will crush the steel hull like a beer can.  What we call crush depth.  Killing everyone on board.  So a sub cannot go too deep.  Which makes going below the surface a delicate and risky business.  To submerge they flood ballast tanks.  Replacing air within the hull with water.  Making it sink.  Other tanks fill with water as necessary to ‘trim’ the boat.  Make it level under water.  When under way they use forward propulsion to maintain depth and trim with control surfaces like on an airplane.  If everything goes well a submarine can sink.  Then stop at a depth below the surface.  And then resurface.  Modern nuclear submarines can make fresh water and clean air.  So they can stay submerged as long as they have food for the crew to eat.

An airplane has no such staying power like a sub.  For planes have nothing to keep them in air but forward propulsion.  So food and water are not as great an issue.  Fuel is.  And is the greatest limitation on a plane.  In the military they have special airplanes that fly on station to serve as gas stations in the air for fighters and bombers.  To extend their range.  And it is only fuel they take on.  For other than very long-range bombers a flight crew is rarely in the air for extended hours at a time.  Some bomber crews may be in the air for a day or more.  But there are few crew members.  So they can carry sufficient food and water for these longer missions.  As long as they can fly they are good.  And fairly comfortable.  Unlike the earlier bomber crews.  Who flew in unpressurized planes.  For it is very cold at high altitudes.  And there isn’t enough oxygen to breathe.  So these crew members had to wear Arctic gear to keep from freezing to death.  And breathe oxygen they carried with them in tanks.  Pressurizing aircraft removed these problems.  Which made being in a plane like being in a tall building on the ground.  Your ears may pop but that’s about all the discomfort you would feel.  If a plane lost its pressurization while flying, though, it got quite uncomfortable.  And dangerous. 

Rapid decompression at altitude can be catastrophic.  And violent.  The higher the altitude the lower the air pressure.  And the faster the air pressure inside the airplane equals the air pressure outside the airplane.  The air will get suck out so fast that it’ll take every last piece of dust with it.  And breathable air.  Oxygen masks will drop in the passenger compartment.  The flight attendants will scramble to make sure all passengers get on oxygen.  As does the flight crew.  Who call in an emergency.  And make an emergency descent to get below 10 thousand feet.  Almost free falling out of the sky while air traffic control clears all traffic from beneath them.  Once below 10 thousand feet they can level off and breathe normally.  But it will be very, very cold.

Man’s Desire is to Go where no Man has Gone before and where no Human Body should Be

Space flight shares some things in common with both submarines and airplanes.  Like airplanes they can’t fly without fuel.  The greatest distance we’ve ever flown in space was to the moon and back.  The Saturn V rocket of the Apollo program was mostly fuel.   The rocket was 354 feet tall.  And about 75% of it was a fuel tank.  In 3 stages.  The first stage burned for about 150 seconds.  The second stage burned for about 360 seconds.  The third stage burned for about 500 seconds (in two burns, the first to get into earth orbit and the second to escape earth orbit).  Add that up and it comes to approximately 16 minutes.  After that the astronauts were then coasting at about 25,000 miles per hour towards the moon.  Or where the moon would be when they get there.  The pull of earth’s gravity slowed it down until the pull of the moon’s gravity sped it back up.  So that’s a lot of fuel burned at one time to hurl the spacecraft towards the moon.  The remaining fuel on board used for minor course corrections.  And to escape lunar orbit.  For the coast back home.  There was no refueling available in space.  So if something went wrong there was a good chance that the spacecraft would just float forever through the universe with no way of returning home.  Much like a submarine that can’t keep from falling in the ocean.  If it falls too deep it, too, will be unable to return home.

Also like in a submarine food and fresh water are critical supplies.  They brought food with them.  And made their own water in space with fuel cells.  It had to last for the entire trip.  About 8 days.  For in space there were no ports or supply ships.  You were truly on your own.  And if something happened to your food and water supply you didn’t eat or drink.  If the failure was early in the mission you could abort and return home.  If you were already in lunar orbit it would make for a long trip home.  The lack of food and hydration placing greater stresses on the astronauts making the easiest of tasks difficult.  And the critical ones that got you through reentry nearly impossible.  Also like on a submarine fresh air to breathe is critical.  Even more so because of the smaller volume of the spacecraft.  Which can fill up with carbon dioxide very quickly.  And unlike a sub a spacecraft can’t open a hatch for fresh air.  All they can do is rely on a scrubber system to remove the carbon dioxide from their cramped quarters.

While a submarine has a thick hull to protect it from the crushing pressures of the ocean an airplane has a thin aluminum skin to keep a pressurized atmosphere inside the aircraft.  Just like a spacecraft.  But unlike an aircraft, a spacecraft can’t drop below 10,000 feet to a breathable atmosphere in the event of a catastrophic depressurization.  Worse, in the vacuum of space losing your breathable atmosphere is the least of your troubles.  The human body cannot function in a vacuum.  The gases in the lungs will expand in a vacuum and rupture the lungs.  Bubbles will enter the bloodstream.  Water will boil away (turn into a gas).  The mouth and eyes will dry out and lose their body heat through this evaporation.  The water in muscle and soft tissue will boil away, too.  Causing swelling.  And pain.  Dissolved nitrogen in the blood will reform into a gas.  Causing the bends.  And pain.  Anything exposed to the sun’s ultraviolet radiation will get a severe sunburn.  Causing pain.  You will be conscious at first.  Feeling all of this pain.  And you will know what is coming next.  Powerless to do anything about it.  Brain asphyxiation will then set in.  Hypoxia.  The body will be bloated, blue and unresponsive.  But the brain and heart would continue on.  Finally the blood boils.  And the heat stops.  In all about a minute and half to suffer and die.

Man is an adventurer.  From the first time we walked away from our home.  Rode the first horse.  Harnessed the power of steam.  Then conquered the third dimension in submarines, airplanes and spacecraft.  We are adventurers.  It’s why we crossed oceans and discovered the new world.  Why we climbed the highest mountains.  And descended to the oceans’ lowest depth.  Why we fly in airplanes.  And travelled to the moon and back.  When things worked well these were great adventures.  When they did not they were horrible nightmares.  While a few seek this adventure most of us are content to walk the surface of the earth.  To feel the sand through our toes.   Or walk to the poolside bar in our flip-flops.  To enjoy an adult beverage on a summer’s day.  While adventurers are still seeking out something new.  And waiting on technology to allow them to go where no man has gone before.  Especially if it’s a place no human body should be.



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