Book Review: The Electra Story

“The Electra Story” by Robert J. SerlingAs 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.

Serling, Robert J. The Electra Story. New York: Bantam Books, [1963] 1991. ISBN 978-0-553-28845-2.

Here is a 1960 promotional film about the Lockheed Electra.

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Saturday Night Science: Fun with Cosmic Rays

I took an international flight today, and did something I’ve intended to do for some time: monitor the background radiation flux as the plane changed altitudes.  I brought along a QuartaRAD RADEX RD1706 Geiger-Müller counter which detects beta particles (high energy electrons) and photons in the x-ray and gamma ray spectra and displays a smoothed moving average of the radiation dose in microsieverts (μSv) per hour.  The background radiation depends upon your local environment: areas with rocks such as granite which are rich in mildly radioactive thorium will have more background radiation than those with rocks such as limestone.

One important component of background radiation is cosmic rays caused by high energy particles striking the Earth’s atmosphere.  The atmosphere is an effective radiation shield and absorbs many of these particles before they reach sea level, but as you go to higher altitudes, fewer particles are absorbed and you experience a higher background radiation dose from cosmic rays.  Background radiation at sea level is usually around 0.10 to 0.13 μSv/h.  At Fourmilab, at an altitude of 806 metres above mean sea level, it usually runs around 0.16 μSv/h.

I waited until the flight was at cruising altitude before turning on the detector and placing it on my tray table near the window of my window seat.  This was not a high-flyer: the plane was a Bombardier Q400 Dash 8 regional turboprop on a medium-range flight within Europe, with a cruising altitude of 7000 metres  (the plane’s service ceiling is 8229 metres, modest compared to the Boeing 747-8’s ceiling of 13,000 m).  My first reading was:

Radiation monitor: 1.24 μSv/h

Wow!  1.24 microsieverts per hour is almost ten times the usual reading near sea level.  And this was inside the fuselage of an airplane cruising at a modest altitude.

About half way through the flight, we encountered moderately high turbulence (enough to turn on the seat belts sign, but nothing really scary), and the pilot in command requested a lower altitude to try to escape it.  Air traffic control approved a descent to 6000 metres.  During the descent, the background radiation level smoothly decreased.  Here is part way down the slope.

Radiation monitor: 0.86 μSv/h

And now we’re at at the new cruising altitude of 6000 m.

Radiation monitor: 0.67 μSv/h

Finally the plane began its descent for landing.  Here are readings on the way down, with the last one on final approach over water shortly before touchdown on the runway on the coast.

Radiation monitor: 0.20 μSv/h

Radiation monitor: 0.13 μSv/h

Now the radiation level has fallen to that around sea level.  But wait, there’s more!

Radiation monitor: 0.07 μSv/h

This is at an altitude of just dozens of metres, still over water, seconds before touchdown.  Background radiation is now around half the usual at sea level.  (This wasn’t a fluke—I got this reading on several consecutive measurement cycles.)  But think about it: the contribution to background radiation from terrestrial sources (such as thorium and uranium in rocks) and cosmic rays are about the same.  But in an airplane flying low over water, the terrestrial component is very small (since the sea has very few radioactive nuclides), so it’s plausible that we’ll see around half the background radiation in such a situation as on terra firma.  Indeed, after landing, the background radiation while taxiing to the terminal went back up to around 0.13 μSv/h.

It would be interesting to repeat this experiment on an intercontinental flight at higher altitude and through higher latitudes, where the Earth’s magnetic field provides less shielding against cosmic rays.  But the unpleasantness of such journeys deters me from making them in anything less that the most exigent circumstances.  There is no original science to be done here: extensive monitoring and analysis of the radiation dose experienced by airline passengers and crews has been done.  This is a Fourmilab “basement science” experiment (well, not in the basement, but in a shrieking aluminium death tube) you can do yourself for amusement.  If you do this on a crowded flight, your seatmate may inquire what’re you’re up to.  “Measuring the cosmic radiation dose we’re receiving on this flight.”  This can either lead to a long and interesting conversation about atmospheric absorption of cosmic rays, background radiation, and radiation hormesis or, more likely, your having an empty seat next to you for the remainder of the flight.  Think of it as win-win.  There were only seven passengers on this flight (I don’t go to places that are too crowded—nobody goes there), so this didn’t come up during this experiment.

Return Flight

A couple of weeks later, the return flight was on an Embraer E190 regional turbofan airliner. The altitude of the flight was never announced en route, but this aircraft has a service ceiling of 12,000 m and usually cruises around 10,000 m, substantially higher than the turboprop I took on the outbound flight. I expected to see a higher radiation level on this flight, and I did.

Return flight: 5.07 μSv/hour

Did I ever! Most of the readings I obtained during cruise were around 3.8 μSv/h, more than thirty times typical sea level background radiation. (I’d show you one of these readings, but there was substantial turbulence on the flight and all of my attempts to photograph the reading are blurred.) During the cruise, I got several substantially higher values such as the 5.07 μSv/h shown above—more than forty times sea level.

Why was there such variation in background radiation during the cruise? I have no idea. If I had to guess, it would be that at the higher altitude there is more exposure to air showers, which might account for the greater variance than observed at sea level or lower altitude in flight. Or, maybe the gremlin on the wing was wearing a radioactive bracelet.

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