The 1977 Dan-Air/IAS Cargo Boeing 707 crash was a fatal accident involving a
Boeing 707-321C
The Boeing 707 is an American, long-range, narrow-body airliner, the first jetliner developed and produced by Boeing Commercial Airplanes.
Developed from the Boeing 367-80 prototype first flown in 1954, the initial first flew on December 20 ...
cargo aircraft operated by
Dan Air Services Limited on behalf of International Aviation Services Limited (trading as
IAS Cargo Airlines
International Aviation Services Limited, trading as IAS Cargo Airlines from 1975, is a defunct wholly privately owned, independentindependent from government-owned corporations British airline that was based at London Gatwick Airport in the Un ...
at the time of the accident), which had been sub-contracted by
Zambia Airways
Zambia Airways is the flag carrier of the Republic of Zambia. The airline is based in Lusaka, Zambia with its hub at Kenneth Kaunda International Airport.
Originally, the airlines was founded in April 1964, however was liquidated by the gover ...
Corporation to operate a weekly scheduled all-cargo service between
London Heathrow
Heathrow Airport (), called ''London Airport'' until 1966 and now known as London Heathrow , is a major international airport in London, England. It is the largest of the six international airports in the London airport system (the others bei ...
and the Zambian capital
Lusaka
Lusaka (; ) is the Capital city, capital and largest city of Zambia. It is one of the fastest-developing cities in southern Africa. Lusaka is in the southern part of the central plateau at an elevation of about . , the city's population was ab ...
via
Athens
Athens ( ; el, Αθήνα, Athína ; grc, Ἀθῆναι, Athênai (pl.) ) is both the capital and largest city of Greece. With a population close to four million, it is also the seventh largest city in the European Union. Athens dominates ...
and
Nairobi
Nairobi ( ) is the capital and largest city of Kenya. The name is derived from the Maasai phrase ''Enkare Nairobi'', which translates to "place of cool waters", a reference to the Nairobi River which flows through the city. The city proper ha ...
. The aircraft crashed during approach to
Lusaka Airport
Lusaka (; ) is the capital and largest city of Zambia. It is one of the fastest-developing cities in southern Africa. Lusaka is in the southern part of the central plateau at an elevation of about . , the city's population was about 3.3 milli ...
,
Zambia
Zambia (), officially the Republic of Zambia, is a landlocked country at the crossroads of Central Africa, Central, Southern Africa, Southern and East Africa, although it is typically referred to as being in Southern Africa at its most cent ...
, on 14 May 1977. All six crew members of the aircraft were killed.
[ (includes picture of accident aircraft one year prior to the accident)]
History of aircraft
The aircraft was a Boeing 707-321C that first entered service with
Pan American World Airways
Pan American World Airways, originally founded as Pan American Airways and commonly known as Pan Am, was an American airline that was the principal and largest international air carrier and unofficial overseas flag carrier of the United States ...
(Pan Am) in 1963. This aircraft was also the first convertible 707 built,
featuring a large freight door on the left-hand side of the forward fuselage, that permitted the carriage of main deck cargo when configured as a freighter. Dan-Air acquired the aircraft in 1976. It was the fourth 707 the UK independent
[the term "independent" in this context denotes private, generally unsubsidised UK airlines that were financially and operationally independent from the ]crown corporation
A state-owned enterprise (SOE) is a government entity which is established or nationalised by the ''national government'' or ''provincial government'' by an executive order or an act of legislation in order to earn profit for the governmen ...
s, i.e. British European Airways
British European Airways (BEA), formally British European Airways Corporation, was a British airline which existed from 1946 until 1974.
BEA operated to Europe, North Africa and the Middle East from airports around the United Kingdom. The a ...
, British Overseas Airways Corporation
British Overseas Airways Corporation (BOAC) was the British state-owned airline created in 1939 by the merger of Imperial Airways and British Airways Ltd. It continued operating overseas services throughout World War II. After the passi ...
and British Airways
British Airways (BA) is the flag carrier airline of the United Kingdom. It is headquartered in London
London is the capital and List of urban areas in the United Kingdom, largest city of England and the United Kingdom, with a populati ...
(prior to privatisation) operated, as well as the type's second
turbofan
The turbofan or fanjet is a type of airbreathing jet engine that is widely used in aircraft engine, aircraft propulsion. The word "turbofan" is a portmanteau of "turbine" and "fan": the ''turbo'' portion refers to a gas turbine engine which ac ...
-powered and second convertible example in service with the airline. At the time of the accident, it had flown about 47,000 hours.
History of flight
The flight was a three-legged originating from
London Heathrow Airport
Heathrow Airport (), called ''London Airport'' until 1966 and now known as London Heathrow , is a major international airport in London, England. It is the largest of the six international airports in the Airports of London, London airport sys ...
to Athens (
Hellinikon Airport), which was uneventful; from Athens it then proceeded to Nairobi (
Jomo Kenyatta International Airport
Jomo Kenyatta International Airport , is an international airport in Nairobi, the capital of and largest city in Kenya. The other three important international airports in Kenya include the Kisumu International Airport,
Moi International Airp ...
). Departure from Nairobi for Lusaka on the final leg occurred as planned at 07:17, 14 May.
The 707 cruised at
flight level 310 for about two hours, after which it was cleared for descent to flight level 110. Flight level 110 was reached at approximately 09:23, and clearance was granted to begin descent towards a target of flight level 70. Just before 09:30, clearance to descend to was granted, and moments later the plane was cleared to make a visual approach to runway 10. A few minutes later, witnesses saw the entire right
horizontal stabiliser
A tailplane, also known as a horizontal stabiliser, is a small lifting surface located on the tail (empennage) behind the main lifting surfaces of a fixed-wing aircraft as well as other non-fixed-wing aircraft such as helicopters and gyroplan ...
and elevator assembly detach from the aircraft. The aircraft subsequently lost pitch control and entered a nose-dive from about to ground level, destroying the aircraft on impact.
There were no survivors among the five crew members and one jumpseat passenger on board the aircraft. There were no other fatalities on the ground. The wreckage was located approximately from the runway.
Investigation
A full investigation was launched by the Zambian authorities and the investigation was then delegated to the UK
Air Accidents Investigation Branch
The Air Accidents Investigation Branch (AAIB) investigates civil aircraft accidents and serious incidents within the United Kingdom, its overseas territories and crown dependencies. It is also the Space Accident Investigation Authority (SAIA) ...
- AAIB. The conclusions made by that investigation are as follows:
It was determined that the structure of the right horizontal stabiliser failed due to
metal fatigue
In materials science, fatigue is the initiation and propagation of cracks in a material due to cyclic loading. Once a fatigue crack has initiated, it grows a small amount with each loading cycle, typically producing striations on some parts o ...
in the rear
spar
SPAR, originally DESPAR, styled as DE SPAR, is a Dutch multinational that provides branding, supplies and support services for independently owned and operated food retail stores. It was founded in the Netherlands in 1932, by Adriaan van Well, ...
structure, and due to the lack of an adequate
fail-safe
In engineering, a fail-safe is a design feature or practice that in the event of a specific type of failure, inherently responds in a way that will cause minimal or no harm to other equipment, to the environment or to people. Unlike inherent safe ...
structure or device should such an event occur. The investigation also identified deficiencies in the assessment of aircraft designs and their certification and in the way aircraft were inspected.
The Boeing 707 320/420 series had an enlarged horizontal stabiliser (tailplane) assembly compared to earlier 707 aircraft, and in the redesign the increased loads on the tailplane structure had been taken by replacing some of the aluminium skinning with
stainless steel
Stainless steel is an alloy of iron that is resistant to rusting and corrosion. It contains at least 11% chromium and may contain elements such as carbon, other nonmetals and metals to obtain other desired properties. Stainless steel's corros ...
. In addition, the spar attachment fittings had been redesigned, making them both stronger and stiffer. This had the unforeseen effect of changing the way the tailplane structure handled gust loads, the stiffer fittings being no longer able to help in absorbing and transferring the
stresses caused by gusts and other normal aerodynamic loads, the flexure (i.e., the
bending
In applied mechanics, bending (also known as flexure) characterizes the behavior of a slender structural element subjected to an external load applied perpendicularly to a longitudinal axis of the element.
The structural element is assumed to ...
loads) of the left and right horizontal stabilizers instead having to be carried by the stabiliser spars entirely by themselves. This led over time to fatigue cracking in the right horizontal stabiliser's rear spar, which, due to the concealed (internal) nature of the tailplane construction, was not noticed by maintenance engineers.
The 707 had been designed to a '
fail-safe
In engineering, a fail-safe is a design feature or practice that in the event of a specific type of failure, inherently responds in a way that will cause minimal or no harm to other equipment, to the environment or to people. Unlike inherent safe ...
' philosophy, and failure of the tailplane rear spar had been calculated to be insufficient to cause the loss of the aircraft, the remaining front spar being sufficiently strong to enable the aircraft to land safely, the damage then being expected to be repaired before the aircraft was re-flown.
However, the accident aircraft had developed a cracked rear right spar without the fault being detected due to its location within part of the structure not normally accessible during routine maintenance, and the aircraft had been flown for a considerable number of hours with the fault present. Over time the crack grew until, it was surmised, the damaged spar was no longer capable of carrying its designed load, whereupon the load was then taken over entirely by the front spar. The accident aircraft encountered several strong gusts during the approach immediately before the accident which, while not dangerous to a structurally sound Boeing 707, exceeded the load capable of being carried by the remaining intact spar on its own, leading to the spar eventually breaking and resulting in complete
structural failure
Structural integrity and failure is an aspect of engineering that deals with the ability of a structure to support a designed structural load (weight, force, etc.) without breaking and includes the study of past structural failures in order to ...
of the entire right horizontal stabiliser.
Tests were conducted to determine whether or not the loss of a single stabilizer was a recoverable situation, and it was determined that recovery would have been possible with action on behalf of the pilots in the form of nose up trim. The wreckage recovered revealed that the elevator trim should have been sufficient to save the aircraft, but further analysis concluded that the failure of the stabilizer was violent enough to fracture the vertical trim jackscrew, which would have resulted in the remaining horizontal stabilizer pitching into a nose down trim position.
The crack found in the failed stabiliser after the accident was thought by investigators unlikely to have been detectable using normal testing means, such as fluorescent dye. It was also thought that the crack had been present for at least 6,000 flight hours before the accident, and before the aircraft had been acquired by Dan-Air from Pan Am.
Inspections of the Boeing 707-300 fleet, made as a result of the crash, found another 38 aircraft with similar cracks.
Notes
References
External links
"Aircraft Accident Report No. 9/78" Air Accident Investigation Branch
The Air Accidents Investigation Branch (AAIB) investigates civil aircraft accidents and serious incidents within the United Kingdom, its overseas territories and crown dependencies. It is also the Space Accident Investigation Authority (SAIA) ...
of the
United Kingdom Department of Transport
*
Report fileArchive
*
AppendicesArchive
Detailed accident description(
ttps://web.archive.org/web/20121019225048/http://www.flightglobal.com/pdfarchive/view/1979/1979%20-%202343.html Archived2009-09-03)
''The Geriatric Jet Problem'', Flight International, 22 October 1977, p. 1201
{{DEFAULTSORT:Dan-Air Boeing 707 Crash
IAS Cargo
Aviation accidents and incidents in Zambia
Airliner accidents and incidents caused by in-flight structural failure
Accidents and incidents involving the Boeing 707
Dan-Air accidents and incidents
May 1977 events in Africa