Lightning & Modern Airliners
fitz
June 2, 2009 http://www.amperefitz.com/aclight.htm
Modern airliners are far more likely to be downed by lightning than
the older airliners that were flying 50 years ago.
I have a pilot license; an airframe and powerplant mechanics license
and before I retired, held a first class radio-telephone license so I
know these facts well that I'm about to relate to you here.
It's all 'fly by wire' today; it wasn't 50 years ago.
The airliner of 50 years ago was built like your car where all the
controls were activated by human muscles plus power steering just like
the steering on most of today's larger cars, trucks and busses. This
method has proven to be reliable for land, sea and air transportation.
Then in the 1960s an entirely new computer oriented method of
controlling the airliner started to manifest itself. This we all knew
as 'fly by wire'.
To the best of my knowledge it began on military aircraft and then
found its way, in a partial method of control, to the Boeing 737
airliner. Now it's the preferred method of total airliner control.
Today virtually all large modern airliners are 'fly by wire' where a
computer actually controls the airplane while also providing a
synthetic feel to the pilot to make him think he is really flying.
There are reasons for this because in many cases the pilot simply
cannot react fast enough: An example of this is 'yaw damp' where
without a yaw damp computerized control, a Pan American 707 airliner
full of people turned completely upside down and was very nearly lost
over the ocean in the early years of sweptback airliner wings.
So we opted for the tremendous strides that computer 'fly by wire'
gave us.
BUT -
- what are the consequences of this method when we look at what
lightning can do to the airliner?
One night, when I was in charge of radio and electrical at Airlift
International, an all cargo DC-8 pulled in and I pushed a tall steel
stand to the aircraft cockpit door. I liked to talk to the crew first
hand about any radio or electrical problems because what they said and
what they actually wrote in the log sometimes differed quite a bit.
One of the crew immediately opened the door and ran down the steps of
the high steel stand saying, "Let me out of this casket!"
He was gone in a flash!
Flying the plane was Captain Applebaum. I knew both him and his wife
very well for years. They both used to come into a store I had on the
circle in Miami Springs, Florida.
Applebaum's DC-8 cargo airliner hit a bad lightning storm over the
Atlantic.
A DC-8 is powered by 110 volt 400 cycle ac delivered from four
alternators on each of the four jet engines. The aircraft's battery
doesn't do much more than light some instrument lights and operate
some relays.
A Lightning strike melted all four fuse-links (pieces of bismuth-
silver metal alloy bigger than a quarter), This meant all 110 volt ac
power was gone!
On the DC-8 everything is actuated by 110 volt ac power.
All the inside lighting was gone. They had to use flashlights.
Applebaum couldn't even switch fuel tanks because all the fuel valves
needed ac to operate. He couldn't even radio out because all that
needed ac as well.
Applebaum was very lucky because this particular DC-8 had come from
Alitalia and they had installed a French artificial horizon that would
run for twenty minutes without ac power.
Applebaum was left with only three other systems that were working and
lit: He had a magnetic compass. He had the four EGT (exhaust gas
temperature) indicators and the four turbine rpm indicators because
they were driven by their own electrical generators.
He had nothing else!
But he successfully flew the airliner this way for twenty minutes
while the co-pilot and flight-engineer left the cabin and used their
flashlights to take down three fiberglass seven foot high panels and
replace the four melted fuse-links, which they luckily had spares for
aboard.
These fuse-links, by the way, were put in to protect the aircraft
alternator wiring from bad exterior power units that, when plugged in,
failed to sync into the aircraft power system. No one had intended
them to melt with lightning but by melting they had indeed saved the
alternator electrical wiring.
After replacing these fuse-links, the flight engineer had to parallel
the four alternators and this entire process completely took up the
twenty minutes that the French artificial horizon was designed to run.
Without that French horizon running for those twenty minutes, they
would have lost the airplane because they were still in the storm.
I know this story is true!
I've told this story many, many times to many, many people in the
aircraft industry and have received laughs and replies that "Lightning
couldn't possibly get inside an airliner to do all that."
But it did do it!
Applebaum came through it because the DC-8 was controlled by muscle
strength that gets put on control cables which actuate the controls
much like the power steering in your car using hydraulic pressure via
the engine driven hydraulic pumps, essentially the same way it's being
done in most vehicles today.
Airliners are simply not controlled that way anymore. The old human
muscle strength plus hydraulic power actuation is 'gone with the
wind'!
Most modern airliners, however, are electrical computerized 'fly by
wire' devices that simply can go completely out of control when all
electrical power is lost.
If you think the airplane battery is going to help, in this situation,
better think again.
Daniel P. Fitzpatrick Jr.
Pilot license # 1195823
Airframe & Powerplant license # 1311098
1st Class Radiotelephone license with RADAR endorsement # P1-7-13647
Also see: http://www.amperefitz.com