Lockheed Electra: Killer Airliner (Part 2)
by Stuart Lee
In Issue #3
, Stuart Lee looked at the mysterious disasters that plagued the Lockheed Electra.
Here, the investigation continues.
While passengers balked at getting on these "flying cylinders of death," the airlines
tried to get around the bad publicity. Eastern touted its "Golden Falcon Service."
National advertised "Jet Powered Service." Braniff called its Electras "L-188s."
(L-188 was the Electra production number, as L-1011 is today for the Lockheed Tristar.)
Meanwhile, the investigations continued. When beautiful new airliners lose their wings for no
And that is what occurred. Boeing lent staff, simulators, and a wind tunnel to Lockheed.
Douglas contributed engineers and equipment; most notably flutter vanes that, when attached to
the ends of the wings, could induce serious oscillation.
The investigation, occurring in the early sixties, was the first serious use of computer stress
analysis in this field.
Electras were test flown in every possible form of turbulence. Test pilots tried to destroy
the Electra by ramming it into the severe Sierra Madre air waves, over and over again. Electras
were put through every possible flight maneuver that would normally cause a wing failure.
Super severe wind tunnel winds were shot out at Electras and mock-ups. Over and over, every
possible test was done to try and break the Electra.
Finally, on May 5, 1960, and engineer stood up at a Lockheed meeting and announced:
"We're pretty sure we've found it."
Basically, the problem was a high-speed aircraft in a conventional design. The Electra's
power plants were housed in four enormous engine nacelles protruding far forward of the straight,
stubby wing. It was the two outboard engines that were involved in the Electra's destruction.
Every aircraft wing is flexible to some degree- some more than others. And wing vibration,
oscillation, or flutter is inherent in the design. Flutter is expected on wings. In engineering
terms, there are more than 100 different types of flutter- or "modes"- in which
metal can vibrate. The "mode" that destroyed the Electras was "whirl mode."
Whirl mode was nothing new. It was not a mysterious phenomenon. As a matter of fact, it is
a form of vibrating motion inherent in any piece of rotating machinery such as oil drills, table fans,
and automobile drive shafts.
The theory was devastatingly simple. A propeller has gyroscopic tendencies. In other words,
it will stay in a smooth plane of rotation unless it is displaced by some strong external force, just as
a spinning top can be made to wobble if a finger is placed firmly against it. The moment such
a force is applied to a propeller, it reacts in the opposite direction.
Now suppose the force drives the propeller upward. The stiffness that is part of its structure
promptly resists the force and pitches the prop forward. Each succeeding upward force is met
by a protesting downward motion. The battle of vibration progresses. The propeller continues to
rotate in one direction, but the rapidly developing whirl mode is vibrating in the opposite direction.
The result, if the mode is not checked, is a wildly wobbling gyroscope that eventually begins to
transmit its violent motion to a natural outlet: the wing.
Whirl mode did occasionally develop in propeller-driver airliners. It always encountered the
powerful stiffness of the entire engine package, the nacelles and the engine mounting, the
mounting being a bar truss holding the engine to the wing. No problem usually. But on painful
microscopic examination of the crash wreckage of the eight Electra engines, it was found that
something caused the engines to loosen and wobble, causing severe whirl mode, which tore off
the Electra's wings. Specifically, the investigation centered on the outboard engines.
What the investigators found was that the engine mounts- made for GE/Allison by the Lord Company-
weren't strong enough to dampen the whirl mode that originated in the outboard engine nacelles.
The oscillation transmitted to the wings caused severe up-and-down vibration, which grew until
the wings tore right off.
The Braniff Electra had an over speeding prop, which produced an eerie, peculiar sound.
When a tape of this sound was played for the crash witnesses, it was absolutely verified as the sound
they heard. Examination of the wreckage found a loose and wobbly prop on the left wing's outboard
engine. Apparently, the whirl mode caused from the wobbly, over speeding prop was unchecked by
the weak engine mounts. The up-and-down motion was transmitted to the Electra's left wing. And it
The Northwest Electra, when landing for its Chicago stop, experienced a "hard landing"
as verified by the lucky few who deplaned there. And all around Tell City, there was known
clear air turbulence. Probably what occurred was that the hard landing and the CAT weakened
the NWA Electra's outboard engines- specifically the engine mounts, causing instigation of whirl
mode, and when the pilot tried to "pull up" and compensate for severe turbulence down
draft, he literally tore off the already weakened wings.
It was discovered that the Lord engine mounts were not strong enough to combat the
destructiveness of whirl mode.
Lockheed embarked on a mass retrofit program called LEAP (Lockheed Electra Adaptation Program).
All Electras had their wings strengthened, their engine nacelles reinforced, and the mounts- which
were originally a bar- became a strong "V", able to withstand much more stress.
That did it. Electras took to the skies with restored energy and speed. And then on October 4, 1960,
an Eastern Electra taking off from Boston to New York crashed into Boston Bay, killing all 72 aboard.
The clamor rose up again to ground the Electras, but it was discovered on examining the
mainly intact wreckage that large numbers of English starlings had been ingested into the
Electra's wide engine intakes. This caused the engines to "flame out." The plane lost
lift, stalled, and fell into the bay. Although this new problem was severe- for all airliners-
it was fortunate in a way that this was a separate problem.
There have been other notable Electra crashes. On September 14, 1960, an American Electra
flipped over upon landing at LaGuardia and hurtled onto the Grand Central Parkway, where it
came to a stop, upside down. All aboard survived. Then on September 17, 1961, another
Northwest Electra crashed near Chicago, killing 37 people.
Neither crash was attributed to any structural flaw in the Electra; the first involved too high a
landing speed and a skid; the second resulted from an improperly replaced aileron cable.
Not too long ago, on January 20, 1985, a Galaxy Airlines Electra on a charter run crashed,
killing about 80 people at Reno-Cannon airport; but this accident was attributed to a stall arising
from the pilot's preoccupation with a clanging fuel port.
Electras continued to serve the airlines into the early eighties, eventually being replaced by jets.
The Navy still flies its submarine chaser version, the Orion.
And if you look in the corners of some large airports, you'll still see an occasional Electra.
A good book on the Electra (which is unfortunately out of print) is "The Electra Story by
Robert Sterling (brother of Rod), published by Doubleday in 1963.