Lightning & Modern Airliners
Lightning & Modern Airliners
June 2, 2009http://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 himthink 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.
- 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 cyclealternating current (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 voltac power was gone!
On the DC-8 everything is actuated by 110 volt ac power. It even powers inverters for the many direct current (dc) needs.
All the inside lighting was gone. They had to use flashlights. Applebaum couldn't even switch fuel tanks because all the fuel valves neededac 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 withoutac 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 no other instruments that worked!
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 ground 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 all this to be a fact. This is absolutely 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. Applebaum's DC-8 ran a full twenty minutes using no electrical power. Your car won't even do that. It needs voltage for the ignition but those jet engines on the DC-8 didn't. They even pumped in their own fuel without needing any electricity whatsoever.
Airliners are simply not constructed nor controlled that way anymore. The old human muscle strength plus hydraulic power actuation -- the way Applebaum did it -- is 'gone with the wind'!
Most modern airliners, instead of using the old human muscle plus hydraulic assist power, are nowelectrical 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.
We gained tremendously by allowing the computer to take over and fly. It controls everything far, far better than humans possibly can.
That is ---- as long as we refrain from going through severe lightning storms.
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