Question: What is the fastest airliner and how fast does it fly?
— submitted by reader James Kriplean, Knoxville, Tenn.
Answer: The Boeing 747 can cruise at 92% of the speed of sound, Mach .92. It is very rarely flown at this speed due to the increased fuel burn required. Most modern jets fly around 80% of the speed of sound, Mach .8.
Q: There's a lot of coverage about the inevitable death of the 747 because it is too costly to operate a four-engine aircraft. Why can't engine manufacturers come up with an engine similar to those on the more fuel-efficient aircraft? For example, producing a version of the engine that is on a 777 to propel the 747?
— Randy, Phoenix
A: The total thrust required is the key, not the number of engines. A 777 engine may be equal to two 747 engines, but the wing is not designed to take such a large engine in one place.
The 747 originally flew in 1969; in those days it took four engines to power it. Therefore, the design was centered on four engines. Since then, engine technology has improved, making more powerful engines common. However the design limitations remain for the 747. The 777, a twin engine airplane, can fly almost as many people, almost as far as a 747, but it was designed thirty years later.
It may be possible to re-engine a 747 to a twin but I have not heard of an economical way.
Q: If the 747-8i could be built with only two Trent 1000 engines, would it sell?
— Joaquin Fraginal, BGC Taguig
A: I believe if Boeing thought a two engine B747-8 would sell, they would build it. Large airplanes are very difficult to sell because of the high initial cost and high cost of operations. Twins like the B777 and A350 provide more economic operations.
Q: It saddens me to see the near-disappearance of the Boeing 747 from active duty. I have always thought of it as the most beautiful aircraft. Are there any planes out of service that you miss?
— Moshe
A: Recently I had the opportunity to fly on three 747s to Europe. It was a pleasure to experience one of the icons of aviation. The 747 revolutionized air travel. I too will be sad to see them retired.
The 727 was a classic. Not many left flying but it remains a beautiful airplane.
My favorite “out of service” airplane has to be Concorde.
John Cox is a retired airline captain with US Airways and runs his own aviation safety consulting company, Safety Operating Systems.
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