Tag Archives: Explosive Decompression

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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21 December 1988

Clipper Maid of the Seas, Pan American World Airways' Boeing 747-121, at Los Angeles International Airport (LAX) 12 March 1987. (Ted Quackenbush via Wikipedia)
Clipper Maid of the Seas, Pan American World Airways’ Boeing 747-121 N739PA, takes off at Los Angeles International Airport (LAX) 12 March 1987. (Ted Quackenbush via Wikipedia)

21 December 1988: Pan American World Airways’ Flight 103 was a scheduled transatlantic passenger flight, originating at Flughafen Frankfurt am Main (FRA) with stopovers at London Heathrow Airport (LHR) and John F. Kennedy International Airport (JFK), with a final destination of Detroit Metropolitan Wayne County Airport (DTW).

The first leg from Frankfurt to London was flown with a Boeing 727. The transatlantic segment of Flight 103 was flown by a Boeing 747-121, N739PA, named Clipper Maid of the Seas. It departed Heathrow at 1825 hours UTC, with 16 crewmembers and 243 passengers. The 747 climbed to the north and leveled off at at 31,000 feet (9,449 meters) at 1856 hours.

At approximately 1903, a time bomb which had been placed inside luggage carried in the airliner’s cargo hold detonated. Explosive decompression magnified the effects of the bomb. The airliner broke into five large sections and fell to the ground at the town of Lockerbie, Scotland.

The impact crater of Boeing 747 N739PA at Sherwood Crescent, Lockerbie. The wings and fuselage center section struck here, 49.5 seconds after the explosion. 200,000 pounds (91,000 kilograms) of jet fuel ignited, destroying many homes. (Martin Cleaver/syracuse.com)
The impact crater of Boeing 747 N739PA at Sherwood Crescent, Lockerbie. The wings and fuselage center section struck here, 49.5 seconds after the explosion. 200,000 pounds (91,000 kilograms) of jet fuel ignited, destroying many homes. (Martin Cleaver/syracuse.com)

All 259 persons on board the 747 were killed, as were another 11 persons on the ground.

The time bomb is believed to have been placed aboard the airliner by agents of the Great Socialist People’s Libyan Arab Jamahiriya, acting on orders of the Brotherly Leader and Guide to the Revolution of Libya, Muammar al-Gaddafi. One of these, Abdelbaset Ali Mohmed al-Megrahi, was convicted of 270 counts of murder in a Scottish criminal court seated in The Netherlands. The defense twice appealed the case, but prior to a decision in the second appeal, al-Megrahi dropped his appeal and asked to be released from jail because it was believed that he would very soon die of cancer. The Scottish court did release him and he returned to Libya on 14 August 2009, on board Colonel Gadaffi’s personal aircraft. He reportedly died 20 May 2012.

Boeing delivered N739PA to Pan American 15 February 1970. The airliner was originally named Clipper Morning Light. At the time of the bombing, it had accumulated 72,464 total flight hours.

The forward section of Clipper Maid of the Seas, near the village of Tundergarth, Scotland.
The forward section of Clipper Maid of the Seas, near the village of Tundergarth, Scotland.

The 747-100 series was the first version of the Boeing 747 to be built. It was operated by a flight crew of three and was designed to carry 366 to 452 passengers. It is 231 feet, 10.2 inches (70.668 meters) long with a wingspan of 195 feet, 8 inches (59.639 meters) and overall height of 63 feet, 5 inches (19.329 meters). The interior cabin width is 20 feet (6.096 meters), giving it the name “wide body.” Its empty weight is 370,816 pounds (168,199 kilograms) and the Maximum Takeoff Weight (MTOW) is 735,000 pounds (333,390 kilograms).

The 747-100 is powered by four Pratt & Whitney JT9D-7A high-bypass ratio turbofan engines. The JT9D is a two-spool, axial-flow turbofan engine with a single-stage fan section, 14-stage compressor (11 high- and 3 low-pressure stages) and 6-stage turbine (2 high- and 4 low-pressure stages). The engine is rated at 46,950 pounds of thrust (208.844 kilonewtons), or 48,570 pounds (216.050 kilonewtons) with water injection (2½-minute limit). This engine has a maximum diameter of 7 feet, 11.6 inches (2.428 meters), is 12 feet, 10.2 inches (3.917 meters) long and weighs 8,850 pounds (4,014 kilograms).

The 747-100 has a cruise speed of 0.84 Mach (555 miles per hour, 893 kilometers per hour) at 35,000 feet (10,668 meters). The maximum certificated operating speed is 0.92 Mach. The airliner’s maximum range is 6,100 miles (9,817 kilometers).

The Boeing 747 has been in production for 48 years. More than 1,536 have been delivered as of September 2017. 205 of these were the 747-100 series. The U.S. Air Force has selected the Boeing 747-8 as the next presidential transport aircraft.

The Names. (StaraBlazkova/Wikipedia)

© 2017, Bryan R. Swopes

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19 April 1955

Lockheed XF-104 Starfighter 083-1002, serial number 53-7787, the second prototype, in flight near Edwards AFB. (Lockheed Martin/Code One Magazine)

19 April 1955¹: Lockheed test pilot Herman Richard (“Fish”) Salmon was flying the second prototype Lockheed XF-104 interceptor, 53-7787, conducting tests of the General Electric T171 Vulcan gun system.

At 47,000 feet (14,326 meters), Salmon fired two bursts from the T171. On the second burst, vibrations from the gun loosened the airplane’s ejection hatch, located beneath the cockpit, resulting in explosive decompression.

Lockheed Chief Test Pilot Anthony W. LeVier (left) and Test Pilot Herman R. Salmon. An F-104 Starfighter is behind them. (Lockheed)
Lockheed Chief Test Pilot Anthony W. LeVier (left) and Test Pilot Herman R. Salmon. An F-104 Starfighter is behind them. (Lockheed Martin)

The Associated Press reported:

Test Pilot Leaps From New Jet

     INYOKERN, Calif., April 20 (AP)—Herman R. (Fish) Salmon, former racing pilot and now a top test pilot, bailed safely from one of the Air Force’s hot new F104 jet fighters over the Mojave dessert [sic] Tuesday.

He was  spotted on the desert after a two-hour search by military planes and brought to the Naval ordinance [sic] test station here for a physical examination. A preliminary checkup indicated he was not injured.

     Salmon, 41, was on a routine test flight when he hit the silk. Authorities gave no hint what happened to the supersecret plane to make the bailout necessary. The craft’s height at the time it was abandoned was not given. The plane’s top speed has been unofficially estimated at 1,200 m. p. h.

     Wreckage of the F104, one of two prototypes now being tested by Lockheed Aircraft Corp. for the Air Force, was found several miles south of the China Lake area.

     A Lockheed spokesman said Salmon, of Van Nuys, Calif., was spotted by a search plane and apparently picked up by a Navy helicopter and flown here. Salmon took off on the test flight from Palmdale, about 70 miles south of here.

Reno Evening Gazette, Volume LXXIX, Number 21, Wednesday, 20 April 1955, Page 24 at Columns 5–7.

Fish Salmon was wearing a David Clark Co. T-1 capstan-type partial-pressure suit and International Latex Corporation (I.L.C. Dover) K-1 helmet for protection in just such an emergency. The capstans are pneumatic tubes surrounded by fabric lacings, running along the arms, torso and legs. As the tubes inflated, the lacings pulled the fabric of the suit very tight and applied pressure to his body as a substitute for normal atmospheric pressure. The partial-pressure garment also enclosed his head, with a fiberglass helmet and a clear visor or face plate providing for vision.

Test pilot Herman R. Salmon with a prototype Lockheed XF-104 parked on Rogers Dry Lake. (Lockheed Martin)
Test pilot Herman R. (“Fish”) Salmon with a prototype Lockheed XF-104, parked on Rogers Dry Lake. (Lockheed Martin)

The sudden loss of cabin pressure and drop to subfreezing temperatures caused Salmon’s face plate to fog over. Inflating air bladders pushed his helmet high on his head.  The cockpit was filled with dust, fiberglass insulation and other debris. All this restricted his visibility, both inside and outside the airplane. The very tight pressure suit restricted his movements.

Fish Salmon cut the throttle, opened the speed brakes and began a descending turn to the left to reach a lower altitude. By the time he had reached 15,000 feet (4,572 meters) he had been unable to find a place on the desert floor to make an emergency landing. It was time to leave the crippled XF-104.

At 250 knots (288 miles per hour/463 kilometers per hour) the ejection seat fired Salmon out of the bottom of the cockpit. He had to open his parachute manually (the seat timer did not operate) and he made a safe landing.

The XF-104 had a downward-firing ejection seat, intended to avoid the airplane's tall vertical tail. Production aircraft used an upward-firing seat. (Lockheed)
The XF-104 had a downward-firing ejection seat, built by Stanley Aviation Inc. It was intended to avoid the airplane’s tall vertical tail. Later production aircraft used an upward-firing Martin-Baker seat. This airplane is the second prototype XF-104, 53-7787. (Lockheed Martin)

The prototype XF-104 impacted the desert approximately 73 miles (117 kilometers) east-northeast of Edwards Air Force Base. It was completely destroyed. Fish Salmon landed about 2 miles (3.2 kilometers) away. He was found two hours later and rescued by an Air Force helicopter.

Occasionally, a satisfied user thanked the researchers at the Aero Medical Laboratory. One of these was Lockheed test pilot Herman R. “Fish” Salmon. On April 14, 1955,¹ Salmon was flying the second XF-104 (53-7787) at 47,500 feet while wearing a T-1 suit, K-1 helmet, and strap-fastened boots. As he triggered the General Electric M61 Vulcan 20 mm cannon for a test firing, severe vibrations loosened the floor-mounted ejection hatch and the cockpit explosively depressurized at the same time as the engine flamed out. The suit inflated immediately. Repeated attempts to restart the engine failed, and Salmon ejected at 15,000 feet. Fish reported, “I landed in a field of rocks ranging from one foot to five feet in diameter. My right arm was injured and my head struck a rock. The K-1 helmet hard shell was cracked, but there was no injury to my head. It took me 10 to 15 minutes to get out of the suit with my injured arm. Rescue was effected [sic] by helicopter approximately two hour after escape.” Salmon reported that the K-1 helmet was excellent for rugged parachute landings, and his only complaint was that the visor may impair vision at extreme altitudes.”

Dressing for Altitude: U.S. Aviation Pressure Suits—Wiley Post to Space Shuttle, by Dennis R., Jenkins, National Aeronautics and Space Administration SP–2011–595, Washington, D.C., 2012, Chapter 4 at Page 141.

Lockheed's Chief Test Pilot, Anthony W. ("Tony") LeVier, is wearing a David Clark Co. T-1 capstan-type partial-pressure suit and K-1 helmet. The first prototype XF-104, 53-7786, is behind him. (U.S. Air Force)
Lockheed’s Chief Test Pilot, Anthony W. (“Tony”) LeVier, is wearing a David Clark Co. T-1 capstan-type partial-pressure suit and International Latex Corporation K-1 helmet. The first prototype XF-104, 53-7786, is behind him. (Jet Pilot Overseas)

There were two Lockheed XF-104 prototypes. Initial flight testing was performed with 083-1001 (USAF serial number 53-7786). The second prototype, 083-1002 (53-7787) was the armament test aircraft. Both were single-seat, single-engine supersonic interceptors. The XF-104 was 49 feet, 2 inches (14.986 meters) long with a wingspan of 21 feet, 11 inches (6.680 meters) and overall height of 13 feet, 6 inches (4.115 meters). The prototypes had an empty weight of 11,500 pounds (5,216 kilograms) and maximum takeoff weight of 15,700 pounds (7,121 kilograms).

The production aircraft was planned for a General Electric J79 turbojet but that engine would not be ready soon enough, so both prototypes were designed to use a Buick-built J65-B-3, a licensed version of the British Armstrong Siddeley Sapphire turbojet engine. XF-104 53-7787 had been built with an afterburning Wright J65-W-7 turbojet, rated at 7,800 pounds of thrust, and 10,200 pounds of thrust with afterburner.

The XF-104 had a maximum speed of 1,324 miles per hour (2,131 kilometers per hour), a range of 800 miles (1,287 kilometers) and a service ceiling of 50,500 feet (15,392 meters).

The General Electric T171 Vulcan was a prototype 6-barrelled 20 mm “Gatling Gun” automatic cannon. The barrels were rotated at high speed by a hydraulic drive. The gun is capable of firing 6,000 rounds per minute. The initial production version was designated M61. The cannon system was installed in a weapons bay on the left side of the F-104, between the cockpit and engine intakes.

The first prototype Lockheed XF-104, 53-7786, was also destroyed, 11 July 1957 when the vertical fin was ripped off by uncontrollable flutter. The pilot, William C. Park, safely ejected.

¹ Reliable sources give the date of this incident as both 14 April and 19 April. Contemporary news reports, published Wednesday, 20 April 1955, say that the accident took place “yesterday” and “Tuesday,” suggesting that the correct date is 19 April.

© 2017, Bryan R. Swopes

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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: South African Airways Flight 201, a chartered British Overseas Airways Corporation de Havilland DH.106 Comet 1, aircraft registration G-ALYY, departed Rome at 1832 UTC, bound for Cairo. The Comet 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.

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 29 feet, 6 inches (8.992 meters). The Comet 1 had a maximum takeoff weight of 110,000 pounds (49,895 kilograms). It was powered by four de Havilland Engine Company Ghost 50 centrifugal flow turbojet engines, producing 5,000 pounds of thrust, each. This gave it a cruising speed of 460 miles per hour (740 kilometers per hour) and cruise altitude of 42,000 feet (12,802 meters). The airliner’s range was 1,500 miles (2,414 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)

© 2016, Bryan R. Swopes

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