Back to home page737 Classic MLG Failures on Landing

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Over the last 17 years there has been at least 24 instances of 737 Classic main landing gear (MLG) failures on landing, see full list below. The causes vary but seem to be due to the following main reasons

  • Excessive shimmy causing failure (7)
  • Heavy landing (3)
  • Component failure under normal load (2)
  • Presence of air in the MLG damper after maintenance (1)
  • Cause unknown (8)

Most of these events have come from shimmy damper failures. The final report of JY-JAQ did an excellent analysis of the causes of shimmy and shimmy damper failure. It cited the following contributory factors:

  • High altitude airport
  • An overly soft landing, allows the landing gears to remain in the air mode longer, which makes them more vulnerable to shimmy
  • Touchdown with a closure rate of 1 fps, which is considered overly soft and may increase the risk of shimmy torsional forces
  • High ground speed at touchdown

For a full list of factors leading to failure issued by Boeing see below:

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*** Updated 14 Nov 2021 ***

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List of known 737 Classic MLG failures:

  • 16 Jun 2022 - 9S-ABJ, 737-300, Gomair, LH MLG collapse landing at Kananga, DR Congo. (cause unknown)
  • 05 Jan 2022 - EP-CAP, 737-400, Caspian Airlines, LH MLG collapse whilst landing at Isfahan, Iran (cause unknown)
  • 20 Mar 2021 - PK-YSF, 737-400SF, Trigana Air Service RH MLG collapse whilst landing at Halim Perdanakusuma Airport, Indonesia (cause unknown)
  • 02 Dec 2020 - EY-560, 737-500, Air Djibouti left MLG collapse at low slow during the landing roll at Garowe, Somalia (cause unknown)
  • 25 Feb 2020 - PK-YSG, 737-300SF, Trigana Air Service, MLG collapse whilst taxying at Jayapura, Indonesia (cause unknown)
  • 22 Nov 2019 - YV-3012, 737-400, Avior Airlines MLG collapse during landing at Bogota (cause unknown)
  • 05 Jun 2019 - HS-KMC, 737-400F, K-Mile Asia at Singapore, main gear torsion link failure on landing (Presence of air in the MLG damper after maintenance)
  • 21 Jan 2019 - 9S-AHJ, 737-300, Serve Air, LH MLG collapse during landing at Kinshasa N'djili, DR Congo (cause unknown)
  • 22 Nov 2018 - OB-2041-P, 737-500, Peruvian Airlines MLG collapse on landing at La Paz. (cause unknown)
  • 28 Mar 2017 - OB-2036-P, 737-300, Peruvian Airlines, Gear collapse and fire on landing at Jauja (shimmy damper)
  • 27 Mar 2017 - EP-TBJ, 737-400, Taban, gear collapse on landing at Ardabil (shimmy damper)
  • 10 Dec 2016 - JY-JAQ, 737-400, Safi Airways, soft Landing and RH MLG collapse at Kabul (shimmy damper)
  • 09 Nov 2016 - HK-5139, 737-400F, AerCaribe partial failure of both left and right main landing-gear landing at Bogota (shimmy damper)
  • 04 Oct 2016 - OE-IAG, 737-400, ASL Airlines, Belfast (shimmy damper)
  • 12 Sep 2016 - PK-YSY, 737-300SF, Trigana Air Service MLG collapse on landing at Wamena, Indonesia. (heavy landing)
  • 26 Nov 2015 - XA-UNM 737-300 Gear collapse on landing at Mexico City-Benito Juárez (cause unknown)
  • 22 Nov 2015 - EX-37005 737-300 Gear collapse on landing at Osh (heavy landing)
  • 26 Oct 2015 - ZS-OAA, 737-400, Comair, Johannesburg, South Africa (shimmy damper)
  • 24 Oct 2015 - OB-2040-P 737-300, Peruvian Airlines MLG collapse on landing at Cusco (shimmy damper)
  • 28 Aug 2015 - PK-BBY 737-300CF, Cardig Air, MLG collapse in a landing accident at Wamena, Indonesia. (heavy landing)
  • 29 Apr 2014 - EI-STD, B737-400, Air Contractors MLG failure on landing at East Midlands (component failure under normal load)
  • 07 Nov 2014 - YA-PIE 737-400, Ariana right MLG failure on landing. (cause unknown)
  • 26 Jan 2014 - ZK-TLC, 737-300SF, Pacific Air Express, MLG collapse on landing at Honiara, Solomon Islands (component failure under normal load)
  • 11 Feb 2013 - AP-BEH, 737-300, Pakistan International Airlines, Muscat-Seeb, Oman (cause unknown)

 

List of causes

Boeing has said that there have been sporadic reports from operators of B737-100/200/300/400/500 aircraft of aircraft MLG vibrations following touchdown and that such vibrations might last for several seconds during the landing roll and might result in broken torsion links, damaged MLG dampers, and even MLG collapses in severe cases. Below is a list of possible factors according to Boeing, in the approximate order of decreasing likelihood:

(a) Excessive wear or free play in the apex joint
• Wear at this location allows undamped torsional free play to exist in the landing gear at the apex joint, which greatly increases the likelihood of shimmy.

(b) Wear or free play in the torsion link bushings (e.g. where the torsion links connect to the outer and inner cylinder of the MLG strut)
• Wear at these locations also allows undamped torsional free play.

(c) Landing with extremely low sink rates
• This type of landing is more likely to experience vibrations than a firmer landing because the torsion links remain in an extended, vertical position which gives the damper less mechanical advantage to perform its function for a longer time period, especially in an asymmetric wheel spin up situation

(d) Presence of air in the MLG dampers
• Several airplane MLG vibration events occurred within a few flights after a new or overhauled damper was installed. In these cases, it was suspected that a thorough bleeding of air from the damper was not performed, thus preventing proper damper operation.

(e) Damper piston fractures
• In a small number of events, it is suspected that the damper piston fractured due to a pre-existing fault (e.g., a fatigue crack).

(f) Over serviced shock strut
• In several events, an over serviced shock strut has been suspected to have been a contributing factor. A shock strut over serviced with nitrogen allows the torsion links to have a reduced mechanical advantage to react to the torsional motion of the inner cylinder.

(g) Incorrect damper installation
• In one event, a damper designed for a very early B737-200 had inadvertently been installed on a later aircraft that required a more heavy-duty damper.

(h) Unconnected hydraulic tube
• In one event, a hydraulic tube for the damper was inadvertently left unconnected after unrelated maintenance, so there was no hydraulic fluid available to the damper.

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