De Havilland Comet


The Comet's story began in 1929, when an officer of the Royal Air Force named Frank Whittle proposed powering an airplane with a gas turbine engine. Rather than applying power to a propeller, this engine would force exhaust gases out the rear of the engine, generating enough force to drive the aircraft forward. Whittle himself described his idea as "something like a giant vacuum cleaner; it sucks air at the front and blows it out at the back." Eleven years of research and experimentation produced Britain's first jet fighter, the Gloster Meteor. By the end of World War II, only one manufacturer had experience building both jet engines and aircraft. The plane was the Vampire, a fighter built by de Havilland. By 1952, the de Havilland Comet, the world's first commercial jetliner went into service and, by all appearances, Great Britain was destined to dominate the changing world of commercial aviation.

The Comet was an immediate sensation, for obvious reasons. Trains and ships were still the dominant means of travel in 1952. Air travel was still a novelty for most travellers. Since World War II meant the temporary suspension of work into newer and faster commercial aircraft, the airliners of the early 1950's were little changed from those of the late 1930's. Even the Douglas DC-7C, the first plane to offer regular non-stop transatlantic service, was little more than a 15 year-old design that had been stretched to carry more passengers and fuel. It's 3,400 horsepower engines, each with 72 cylinders, were noisy and produced unpleasant vibrations inside the passenger compartment. Imagine the surprise then, when the de Havilland Comet made its appearance in 1952. It had no obvious means of propulsion; it's four jet engines were built inside the wings. Rather than the usual sound of piston engines, people heard an unfamiliar howling sound as the Comet rolled down the runway. Instead of a 40 hour flight to Johannesburg, South Africa, the Comet could fly from London to Johannesburg , via Rome, Beirut and Khartoum, in 23 hours, at speeds up to 500 MPH. Rather than lumbering through storms, the Comet flew above the weather, eight miles up in the stratosphere. Its air-conditioned, fully pressurized cabin provided passengers with a quiet, smooth ride previously unheard of in commercial aviation.

During its first year of operation, the Comet carried 28,000 passengers a total of 104 million miles. By May 1953, de Havilland had firm orders for 50 Comets from the world's airlines and was negotiating for 100 more. The Comet was such a sensation the Queen Mother and Princess Margaret flew one from London to Rhodesia. The Comet was an unqualified success and, by all appearances, Great Britain was poised to dominate commercial aviation for the next forty years. As the editor of American Aviation Magazine said, "Whether we like it or not, the British are giving the U.S. a drubbing in jet transport." And then the accidents began.

The first two accidents, in 1953, occurred on takeoff. In the first, the plane failed to become airborne. The accident was blamed on pilot error and no one was killed. The second accident, however, left no survivors and appeared to be caused by a design flaw in the airplane. A modification would be made to the wings that allowed for greater lift at low speeds. A third accident occurred as a Comet crashed on takeoff from Calcutta. This accident was blamed on turbulence and no fault was found with the plane. The public's confidence in the Comet was undiminished - until January 10, 1954.

A BOAC Comet departing from Rome climbed to 26,000 feet, en route to its assigned altitude of 36,000 feet. Captain Alan Gibson began to radio a message to another BOAC plane behind him. "Did you get my . . ." Silence. Seconds later, fishermen near the island of Elba saw the remains of the Comet plunge into the sea.

The Comets were grounded while de Havilland and the British government searched for the cause of the disaster. Unfortunately, with the plane in thousands of pieces beneath 500 feet of water, the investigators had little to go on. Speculation ranged from sabotage to clear-sky turbulence to an explosion of vapour in an empty fuel tank. While the Royal Navy utilized sonar, divers and underwater television cameras to salvage as many parts of the plane as possible, the investigators utilized what limited information they had and recommended 50 modifications to the remaining Comets that would, they hoped, correct whatever problem had destroyed the BOAC flight. Basically, they were guessing. The modifications included the installation of shields between the engines and fuel tanks, reinforced fuel lines and new smoke detectors. Less than two months later, with the modifications in place, the Comets again took to the skies. The engineers crossed their fingers, hoping their shotgun approach had found the real culprit. It hadn't. Sadly, only two weeks after resuming service, another BOAC Comet disappeared. The plane had departed Rome on its way to Cairo and was climbing to its assigned altitude of 35,000 feet when, suddenly, radio contact ceased. There were no eye-witnesses. Once again, the Comets were grounded.

Meanwhile, the Royal Navy had succeeded in salvaging about two-thirds of the Comet from the first disappearance. The wreckage suggested that the cabin itself had failed. There were traces of blue on the vertical stabilizer or tail of the plane. Chemical analysis showed them to have come from the seats, suggesting that some force had hurled the contents of the cabin against the tail. Paint from the fuselage was found on the left wing. The conclusion was inescapable - explosive decompression of the cabin. But why? How had the designers failed? The Comet was the most thoroughly tested passenger plane ever built. The engineers at de Havilland knew the Comet would have to withstand changes in pressurization that no piston-powered airliner had ever encountered. They had built a decompression chamber to test the cabin of the new airliner. They manipulated pressures inside and outside the cabin to simulate conditions the Comet would experience in the thin, cold air at 38,000 feet. One test cabin was subjected to this test 2,000 times and passed with flying colors. After all this testing, why were the planes blowing apart in actual flight?

The Ministry of Civil Aviation decided upon a unique test to find out. They built a tank large enough to hold one of the grounded Comets. The wings protruded from water-tight slots in the sides of the tank. Then the tank and cabin were flooded with water. The water pressure inside the cabin would be raised to eight and a quarter pounds per square inch to simulate the pressure encountered by a Comet at 35,000 feet. It would be held there for three minutes and then lowered while the wings were moved up and down by hydraulic jacks. The hydraulic jacks would simulate the flexing that naturally occurs in aircraft wings during flight. This process continued non-stop, 24 hours a day. This torture test continued until the cabin in the tank had been subjected to the stresses equivalent to 9,000 hours of actual flying. Suddenly, the pressure dropped. The water was drained and the fuselage examined. The investigators were horrified to find a split in the fuselage. It began with a small fracture in the corner of an escape hatch window and extended for eight feet. Metal fatigue! Had the Comet not been under water, the cabin would have exploded like a bomb. Several months later the results of this test were corroborated when an Italian trawler recovered a large section of cabin roof from the sea. A crack had started in the corner of a navigation window on top of the fuselage. Like the escape hatch window of the test Comet, it had square corners. The square design of the windows was the major flaw that doomed the Comet. Strangely, the U.S. Civil Aeronautics Administration, predecessor to the FAA, had misgivings about the square windows of the Comet several years earlier and refused to grant it an air-worthiness certificate so it could fly in the United States.

The bottom line? Aside from the square windows, de Havilland's testing of the new plane while still in its design phase was inadequate. They had limited the new cabin to static testing alone, meaning they had subjected the cabin to pressurization, but neglected to add in the effects of motion, such as flexing of the airframe and wings. No one at de Havilland had anticipated the effects on the airframe of an airliner that would climb to altitude as quickly as the jet-powered Comet. Like the Titanic forty years earlier, the Comet suffered design flaws that sealed its fate before its first flight. It would be four full years before the Comet would be re-engineered sufficiently to once again take to the skies. But by then it was too late. The Boeing 707 had already gone into service. The newer 707 could carry twice as many passengers as the Comet and had a greater range. The word's airlines began ordering 707s and the Comet, along with its maker, were doomed to oblivion. The 707 went on to become one of the safest, most successful airliners of all time.

Dimensions (Comet 1)
Length 93 ft 10 in 28.61 m
Wingspan 114 ft 9 in 34.98 m
Height 29 ft 6 in 9 m
Wing area 2,023 ft 188.3 m

Weights
Empty lb kg
Loaded 105,000 lb 47,600 kg
Maximum takeoff lb kg
Capacity 36-44 passengers

Powerplant
Engines 4 de Havilland Ghost 50 turbojets
Thrust (each) 5,000 lbf 22.2 kN

Performance
Maximum speed 450 mph 725 km/h
Range 1,500 mi 2,400 km
Ferry range km miles
Service ceiling 42,000 ft 12,800 m
Rate of climb ft/min m/min

Dimensions
Dimensions (Comet 4)
Length 111 ft 6 in 34.0 m
Wingspan 114 ft 10 in 35.0 m
Height 29 ft 6 in 9.0 m
Wing Area 2,121 ft 197 m

Weights
Empty 75,400 lb 34,200 kg
Loaded 162,000 lb 73,470 kg
Maximum takeoff lb kg
Capacity 56-109 passengers

Powerplant
Engine 4 Rolls-Royce Avon Mk 524 turbojets
Thrust (each) 10,500 lbf 46.8 kN

Performance
Maximum speed 500 mph 805 km/h
Range 3,225 miles 5,190 km
Ferry range km miles
Service ceiling 40,000 ft 12,200 m
Rate of climb ft/min m/min