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Thursday, December 28, 2017

Reading List: The Electra Story

Serling, Robert J. The Electra Story. New York: Bantam Books, [1963] 1991. ISBN 978-0-553-28845-2.
As the jet age dawned for commercial air transport, the major U.S. aircraft manufacturers found themselves playing catch-up to the British, who had put the first pure jet airliner, the De Havilland Comet, into service in 1952, followed shortly thereafter by the turboprop Vickers Viscount in 1953. The Comet's reputation was seriously damaged by a series of crashes caused by metal fatigue provoked by its pressurisation system, and while this was remedied in subsequent models, the opportunity to scoop the Americans and set the standard for passenger jet transportation was lost. The Viscount was very successful with a total of 445 built. In fact, demand so surpassed its manufacturer's production rate that delivery time stretched out, causing airlines to seek alternatives.

All of this created a golden opportunity for the U.S. airframers. Boeing and Douglas opted for four engine turbojet designs, the Boeing 707 and Douglas DC-8, which were superficially similar, entering service in 1958 and 1959 respectively. Lockheed opted for a different approach. Based upon its earlier experience designing the C-130 Hercules military transport for the U.S. Air Force, Lockheed decided to build a turboprop airliner instead of a pure jet design like the 707 or DC-8. There were a number of reasons motivating this choice. First of all, Lockheed could use essentially the same engines in the airliner as in the C-130, eliminating the risks of mating a new engine to a new airframe which have caused major troubles throughout the history of aviation. Second, a turboprop, although not as fast as a pure jet, is still much faster than a piston engined plane and able to fly above most of the weather. Turboprops are far more fuel efficient than the turbojet engines used by Boeing and Douglas, and can operate from short runways and under high altitude and hot weather conditions which ground the pure jets. All of these properties made a turboprop airliner ideal for short- and medium-range operations where speed en route was less important than the ability to operate from smaller airports. (Indeed, more than half a century later, turboprops account for a substantial portion of the regional air transport market for precisely these reasons.)

The result was the Lockheed L-188 Electra, a four engine airliner powered by Allison 501-D13 turboprop engines, able to carry 98 passengers a range of 3450 to 4455 km (depending on payload mass) at a cruise speed of 600 km/h. (By comparison, the Boeing 707 carried 174 passengers in a single class configuration a range of 6700 km at a cruise speed of 977 km/h.)

A number of U.S. airlines saw the Electra as an attractive addition to their fleet, with major orders from American Airlines, Eastern Air Lines, Braniff Airways, National Airlines, and Pacific Southwest Airlines. A number of overseas airlines placed orders for the plane. The entry into service went smoothly, and both crews and passengers were satisfied with the high speed, quiet, low-vibration, and reliable operation of the turboprop airliner.

Everything changed on the night of September 29th, 1959. Braniff Airways flight 542, an Electra bound for Dallas and then on to Washington, D.C. and New York, disintegrated in the skies above Buffalo, Texas. There were no survivors. The accident investigation quickly determined that the left wing of the airplane had separated near the wing root. But how, why? The Electra had been subjected to one of the most rigorous flight test and certification regimes of its era, and no problems had been discovered. The flight was through clear skies with no violent weather. Clearly, something terrible went wrong, but there was little evidence to suggest a probable cause. One always suspects a bomb (although less in those days before millions of medieval savages were admitted to civilised countries as “refugees”), but that was quickly ruled out due to the absence of explosive residues on the wreckage.

This was before the era of flight data recorders and cockpit voice recorders, so all the investigators had to go on was the wreckage, and intense scrutiny of it failed to yield an obvious clue. Often in engineering, there are mysteries which simply require more data, and meanwhile the Electras continued to fly. Most people deemed it “just one of those things”—airliner crashes were not infrequent in the era.

Then, on March 17th, 1960, in clear skies above Tell City, Indiana, Northwest Airlines flight 710 fell out of the sky, making a crater in a soybean field in which almost nothing was recognisable. Investigators quickly determined that the right wing had separated in flight, dooming the aircraft.

Wings are not supposed to fall off of airliners. Once is chance, but twice is indicative of a serious design or operational problem. This set into motion one of the first large-scale investigations of aircraft accidents in the modern era. Not only did federal investigators and research laboratories and Lockheed invest massive resources, even competitors Boeing and Douglas contributed expertise and diagnostic hardware because they realised that the public perception of the safety of passenger jet aviation was at stake.

After an extensive and protracted investigation, it was concluded that the Electra was vulnerable to a “whirl mode” failure, where oscillations due to a weakness in the mounting of the outboard engines could resonate with a mode of the wing and lead to failure of its attachment point to the fuselage. This conclusion was highly controversial: Lockheed pointed out that no such problem had been experienced in the C-130, while Allison, the engine manufacturer, cited the same experience to argue that Lockheed's wing design was deficient. Lawsuits and counter-suits erupted, amid an avalanche of lawsuits against Lockheed, Allison, and the airlines by families of those killed in the accidents.

The engine mountings and wings were strengthened, and the modified aircraft were put through a grueling series of tests intended to induce the whirl mode failures. They passed without incident, and the Electra was returned to service without any placard limitations on speed. No further incidents occurred, although a number of Electras were lost in accidents which had nothing to do with the design, but causes all too common in commercial aviation at the time.

Even before the Tell City crash, Lockheed had decided to close down the Electra production line. Passenger and airline preference had gone in favour of pure jet airliners (in an age of cheap oil, the substantial fuel economy of turboprops counted less than the speed of pure jets and how cool it was to fly without propellers). A total of 170 Electras were sold. Remarkably, almost a dozen remain in service today, mostly as firefighting water bombers. A derivative, the P-3 Orion marine patrol aircraft, remains in service today with a total of 757 produced.

This is an excellent contemporary view of the history of a controversial airliner and of one of the first in-depth investigations of accidents under ambiguous circumstances and intense media and political pressure. The author, an aviation journalist, is the brother of Rod Serling.

The paperback is currently out of print but used copies are available, albeit expensive. The Kindle edition is available, and is free for Kindle Unlimited subscribers. The Kindle edition was obviously scanned from a print edition, and exhibits the errors you expect in scanned text not sufficiently scrutinised by a copy editor, for example “modem” where “modern” appeared in the print edition.

Posted at December 28, 2017 03:09