Ask the Captain: Questions about three-engine jets - CBS News 8 - San Diego, CA News Station - KFMB Channel 8

Ask the Captain: Questions about three-engine jets

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Three-engine airplanes such as the Lockheed L-1011 were built when jet engines had less thrust than today's twin-engine long-haul models. Three-engine airplanes such as the Lockheed L-1011 were built when jet engines had less thrust than today's twin-engine long-haul models.

Question: Are trijet aircraft less safe than twin-engine or four-engine aircraft?

- Andrew, Scottsdale, Arizona

Answer: No. Trijets are safe. But modern twin-engine aircraft have such reliable engines that pilots can fly their entire career without experiencing an engine failure.

Older passenger jets were built with three or four engines because they needed the combined thrust when engine technology was not as advanced as it is today. Airplanes such as the B777 have engines producing more than 110,000 pounds of thrust. These highly reliable high-thrust engines have reduced the need for additional engines.

A few airplanes still have four engines, such as the Airbus A380, but they are now the exception.

Q: Years ago I was on a DC-10 for Cleveland which couldn't get up to desired cruise altitude because the outside temperature at 25,000 was 70 degrees. The poor jet just lumbered, unable to climb higher. Does this happen very often?

- Rob Palmer, Bangor, Maine

A: The standard temperature for 25,000 feet is -34.5 C (-30 F). Seventy degrees Fahrenheit at that altitude would be 100 degrees warmer than normal, a variation so extreme it seems likely you've misremembered it. But the issue you've described is real: Warm air does decrease performance, and the warmer the air, the lower an airplane's cruise altitude at maximum weight.

Q: What is Maneuver Load Elimination?

- Tom, Savannah, Georgia

A: During flight, there are various loads (forces) on the airplane. One of them is gravity. Newer airplanes use powerful computers to recognize increasing G load on the airplane and to reduce it by deflecting flight control surfaces. This technology has been available for many years (the Lockheed L1011 had it). It not only improves the ride for the occupants, it reduces stress on the airplane.

Q: Many movies depict lots of open space under the cabin floor of 747s and similar large aircraft. Is there a large workspace or kitchen area in that area or is it generally completely full of cargo containers?

- Russ, Virginia

A: The L1011 had a galley under the main deck. In recent times, some airplanes have crew rest facilities below the main deck.

In most airplanes, there are only cargo containers below the main deck.

Q: Do any airlines still use the L1011?

- John, Park Ridge, Illinois

A: No, none are still flying for commercial airlines. The L1011 was technologically advanced when it debuted in 1972, but more modern and efficient airplanes have replaced it in airline fleets.

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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