Tag Archives: Metal Fatigue

8 April 1954

De Havilland DH.106 Comet 1 G-ALYY, 1953. (Zoggavia)
De Havilland DH.106 Comet 1 G-ALYY, 1953. (Zoggavia)

8 April 1954: Suid-Afrikaanse Lugdiens (South African Airways) Flight 201, a chartered British Overseas Airways Corporation de Havilland DH.106 Comet 1, departed Rome at 1832 UTC, bound for Cairo.

The Comet, registered G-ALYY, was under the command of Captain Wilhelm K. Mostert, with First Officer Barent J. Grove, Navigator Albert E. Sissing, Radio Officer Bertram E. Webstock, and Flight Engineer August R. Lagesen. Air Hostess Pamela L. Reitz and Flight Steward Jacobus B. Hok were in the passenger compartment with the 14 passengers.

As the airliner climbed toward 35,000 feet (10,668 meters), they made several position reports. Last heard from at 1907 UTC, radioing an expected arrival time at Cairo, the Comet disintegrated in flight and fell into the Tyrrhenian Sea. Searchers found a debris field and floating bodies the next day near the volcanic island of Stromboli. All 21 persons aboard were killed.

This was the second catastrophic failure of a DH.106 in just three months. BOAC immediately grounded its entire Comet fleet, and the British Air Ministry revoked the airliner’s certificate of airworthiness. Production of the airliner at de Havilland was halted.

The first crash had been presumed to be a result of an in-flight fire, and the second, an uncontained turbine engine failure. But an extensive investigation eventually determined that the cause of both crashes was the in-flight break up of the fuselage pressure hull. Metal fatigue of the fuselage was caused by the repeated expansion and contraction of pressurization cycles. Cracks in the aluminum skin formed at corners of the passenger compartment windows and then spread outward. This resulted in catastrophic explosive decompression.

Cut-away illustration of de Havilland Comet I G-ALYP by artist Laurence Dunn.

The DH.106 Comet 1 was the first production version and was very similar to the two prototypes. It can be visually identified by its square passenger windows. It was flown by a pilot, co-pilot, flight engineer and navigator. The airliner could carry up to 44 passengers.

The airplane was 93 feet (28.346 meters) long with a wingspan of 115 feet (35.052 meters) and overall height of 27 feet, 10 inches (8.484 meters). The wings were swept 20°, as measured at ¼ chord. The fuselage had a maximum outside diameter of 10 feet, 3 inches (3.124 meters), and 9 feet, 9 inches (2.972 meters) inside. The Comet 1 had an authorised maximum all-up weight of 107,000 pounds (48,534 kilograms).

The Comet I was powered by four de Havilland Engine Co., Ltd., Ghost 50 Mk.I turbojet engines. The Ghost was a single-shaft centrifugal-flow turbojet with a single-stage compressor, 10 combustion chambers and a single-stage turbine. It was rated at 5,000 pounds of thrust (22.24 kilonewtons) at 10,250 r.p.m. The Ghost 50 had a maximum diameter of 4 feet, 5 inches (1.346 meters), length of 10 feet, 1 inch (3.073 meters) and dry weight of 2,218 pounds (1,006 kilograms). When first placed in service, the engines required a combustion chamber inspection at 125 hour intervals. A complete overhaul was required every 375 hours. The Ghost was the first turbojet certified for civil airliner operations.

A de Havilland Engine Company advertisement in the Illustrated London News, circa 1950.

The Comet I had a maximum cruising speed of 490 miles per hour (789 kilometers per hour), True Air Speed, and operating altitude of 35,000 to 40,000 feet (10,668–12,192 meters). The airliner’s fuel capacity was 6,050 Imperial gallons (27,504 liters, or 7,266 U.S. gallons) giving a practical stage length of 2,140 miles (3,444 kilometers). The maximum range was 3,860 miles (6,212 kilometers).

Twelve DH.106 Comet 1 airliners were built.

The de Havilland Comet was the first commercial jet airliner and its introduction had revolutionized the industry. The two disasters were a blow from which the company never really recovered.

The first production de Havilland DH.106 Comet 1, G-ALYP, in formation with the two prototypes, G-ALVG and G-ALZK. G-ALYP also broke up in flight, 10 January 1954. (Ed Coates Collection)
The first production de Havilland DH.106 Comet 1, G-ALYP, in formation with the two prototypes, G-ALVG and G-ALZK. G-ALYP also broke up in flight, 10 January 1954. (Ed Coates Collection)

© 2019, Bryan R. Swopes

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10 January 1954

The first production de Havilland DH.106 Comet 1, G-ALYP, in formation with the two prototypes, G-ALVG and G-ALZK. G-ALYP also broke up in flight, 10 January 1954. (Ed Coates Collection)
The first production de Havilland DH.106 Comet 1, G-ALYP, in formation with the two prototypes, G-ALVG and G-ALZK. (Ed Coates Collection)

10 January 1954: British Overseas Airways Corporation Flight 781 departed Ciampino Airport, Rome, Italy, at 0931 UTC, enroute to Heathrow Airport, London, England. The airliner was the first production de Havilland DH.106 Comet I, G-AYLP, serial number 06003. The flight crew were Captain Alan Gibson, First Officer William John Bury, Engineer Officer Frances Charles McDonald and Radio Officer Luke Patrick McMahon. There were two flight attendants, Frank L. Saunders and Jean Evelyn Clark, and 29 passengers. After departure began climbing toward its cruise altitude of 27,000 feet (8,230 meters).

At 0951 UTC, 20 minutes after takeoff, Captain Gibson was conversing by radio with another BOAC flight. It is presumed that Flight 781 had reached its cruise altitude. Captain Gibson was heard to say, “George How Jig from George Yoke Peter [the phonetic alphabet call signs for Argonaut G-ALHJ and Comet G-AYLP] did you get my—” and the transmission suddenly ended. Nothing more was heard from Flight 781 and it did not arrive at its destination.

Several fishermen had seen the airliner crash into the Mediterranean Sea near the island of Elba and recovered bodies of the victims, which were found to have suffered the effects of explosive decompression.

Wreckage of Comet G-AYLP was found on the sea floor, 12 February 1954, and it was apparent that the airliner had broken up in flight. Consideration was given to the possibility of a bomb having been placed aboard, or that an uncontained turbojet engine failure had penetrated the pressure cabin resulting in a structural failure of the fuselage through explosive decompression.

De Havilland Comet 1 G-AYLP (Crash-aerien)
De Havilland Comet 1 G-AYLP (www.crash-aerien.news)

After two prototypes, G-AYLP was the first production Comet. It was the fourth DH.106 to be lost in just over fourteen months. With the cause of Flight 781’s crash undetermined, B.O.A.C. grounded its remaining Comet airliners. De Havilland engineers recommended more than 60 modifications to improve perceived weaknesses in the Comet fleet.

Extensive testing by the Royal Aircraft Establishment determined that the Comet’s pressurized fuselage could be expected to fail from metal fatigue after 1,000 pressurization/depressurization cycles. G-AYLP had experienced 1,290 pressurization cycles during the 3,681 hours it had flown since its first flight, 9 January 1951.

The Royal Aircraft Establishment placed DH.106 Comet I G-AYLU in a water tank to conduct pressurization tests. (lessonslearned.faa.gov)
The Royal Aircraft Establishment placed DH.106 Comet I G-AYLU in a water tank to conduct pressurization tests. (lessonslearned.faa.gov)

Reconstruction of G-ALYP’s fuselage revealed that a fatigue crack had begun at a rivet hole of a square opening for the airplane’s automatic direction finder antenna. With the differential in pressure from inside and outside the passenger cabin, this crack had spread along the top of the fuselage through a passenger window and back to to the elevators at the tail. The fuselage structure then failed explosively and the airplane’s tail section came off. The wings then failed and fuel carried inside caught fire. The cockpit section tore away from the remaining fuselage section.

In reporting the Probable Cause of the destruction of G-AYLP, the committee wrote,

We have formed the opinion that the accident at Elba was caused by structural failure of the pressure cabin, brought about by fatigue. We reach this opinion for the following reasons:

(i) The low fatigue resistance of the cabin has been demonstrated by the test described in Part 3, and the result is interpretable as meaning that there was, at the age of the Elba aeroplane, a definite risk of fatigue failure occurring.

(ii) The cabin was the first part of the aeroplane to fail in the Elba accident.

(iii) The wreckage indicates that the failure in the cabin was the same basic type as that produced in the fatigue test.

(iv) This explanation seems to us to be consistent with all the circumstantial evidence.

(v) The only other defects found in the aeroplane were not concerned at Elba, as demonstrated by the wreckage. Report of the Public Inquiry into the causes and circumstances of the accident which occurred on the 10th January 1954, to the Comet aircraft G-AYLP.

Four months later, April 8 1954, a Comet 1 operated by South African Airways as Flight 201 from Rome to Cairo, G-ALYY, crashed near Naples, Italy with the deaths of all 21 persons aboard. The airplane had explosively broken up at an altitude of 35,000 feet (10,668 meters).

The de Havilland DH.106 Comet fleet was grounded and the Ministry of Transportation withdrew the type’s Certificate of Airworthiness. Production of the airliner at Hatfield came to a stop.

BOAC's DH.106 Comet I G-ALYW in long term storage at Heathrow, 12 September 1954. (RuthAS via Wikipedia)
BOAC’s DH.106 Comet I G-ALYW in long term storage at Heathrow, 12 September 1954. (RuthAS via Wikipedia)

De Havilland redesigned the Comet, and as the Comet 4 it had a successful career in airline operation. It eventually lost out to the faster, longer range Boeing 707 and Douglas DC-8. Production ceased in 1964 and B.O.A.C. retired its last Comet in 1965.

The Comet was again redesigned as the Hawker Siddeley Nimrod maritime reconnaissance aircraft.

© 2016, Bryan R. Swopes

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