KLM B772 at Osaka on Sep 23rd 2017, dropped panel on climb out
Last Update: January 10, 2019 / 22:51:30 GMT/Zulu time
Japan's Ministry of Transport reported the panel originated from the right hand wing's root fairing, size about 1 meter by 0.6 meters (3 feet by 2 feet) and weighing about 4 kg/9 lbs, separated when the aircraft was climbing through approximately 2500 meters (8000 feet). The JTSB have opened an investigation into the occurrence rated a serious incident.
The airline reported a fairing panel, size about 1 square meter, was lost and landed in the city of Osaka. Damage to a car was reported, there were no injuries. The aircraft was able to safely continue the flight to Amsterdam. The airline is cooperating with Japan's Civil Aviation Authority and Boeing to investigate the occurrence.
On Sep 25th 2017 the JTSB reported the panel, size 1m by 0.6m weighing 4.3kg (3 feet by 2 feet weight 9.4lbs), originated from the root fairing above the trailing edge of the right hand wing. The panel impacted a car driving on Keihan National Highway near Chome 3. The occurrence, that is being compared to a situation that dropped from an aircraft and collided with a person, is being investigated.
On Nov 7th 2017 the JTSB reported in a press release that the investigation is still ongoing. So far it has been established that the bracket securing panel 198AR above the right hand wing root had fractured. All bolts were still present on the fuselage, however wrong bolts had been used (BACB30XD3K5 instead of the correct BACB30LH3-4). Traces on the holes of the panel suggest the bolts and screws passed through the panel's holes.
On Jan 10th 2019 the JTSB released their final report concluding the probable causes of the serious incident were:
It is certain that this serious incident occurred when the departed right aft wing-to-body fairing panel struck and damaged a moving vehicle, while the aircraft was climbing and passing over the city of Osaka after takeoff.
Regarding the departure of the Panel, it is highly probable that the Bracket that secured the Panel’s forward upper corner by holding it to the Aircraft’s side broke, a gap was occurred between the Panel’s forward upper corner and the fuselage, and the Panel departed due to the pressure of inflowing air and vibration.
The JTSB analysed:
It is probable that the Panel was not fitted tightly to the fuselage because the preload that forces the forward upper corner of the Panel down was weak or had weakened because the Bracket was a pre-enhancement Bracket that was manufactured with a bending process and its dimension accuracy was insufficient, meaning that it also had insufficient strength. It is probable that, because of this, a gap was created between the forward upper corner of the Panel and the fuselage and air flowed in behind the Panel. It is probable that protective film on the inboard side of the forward upper corner of the Panel was peeled off by the inflowing air.
Given that marks caused by fatigue fracture were left on the broken Bracket’s fractured surfaces, it is probable that load was placed on the Bracket and bolts by the air flowing inside the Panel that was in addition to the load caused by ordinary aerodynamic force from the Panel’s exterior, and that repetition of this force to create repeated bending stress on the Bracket’s flanges and led to fatigue fracture.
From the above, it is highly probable that the Bracket broke and an even larger gap formed between the forward upper corner of the Panel and fuselage, and the Panel departed due to the pressure of inflowing air and vibration.
Replacement with Enhanced Brackets
Given that the enhanced Brackets have greater strength and higher dimension accuracy, it is probable that replacement with the enhanced Brackets is an effective means of preventing the departure of similar panels. Moreover, thus far, there have been no reports of damage to the Brackets or departure by similar panels on aircraft on which the enhanced Brackets were installed.
As was described in 2.7 (10), the Aircraft’s manufacturer received reports of damage to the pre-enhancement Brackets and departure of similar panels, and it issued two service bulletins (SB) providing prevention measures. However, these SBs applied to -300 Aircraft and -300 ER Aircraft. It is somewhat likely that they did not apply to -200 Aircraft because noticeable failures were discovered on -300 Aircraft and -300ER Aircraft in inspections conducted by the Aircraft’s manufacturer.
Moreover, as was described in 2.7 (11), the Aircraft’s manufacturer received reports of damage to the Brackets from operators of aircraft of the same type and series, and it developed an enhanced Bracket and provided information on it to operators via a service letter (SL). However, because no SB providing instructions replacement to the enhanced Brackets was issued¸ the Operator did not make plans to make replacements to the enhanced Brackets.
When the similar panel departs the aircraft, it could result in damage to the airplane or a potential hazard to persons or property on the ground. Thus, in order to prevent the occurrence of similar cases, the Aircraft’s manufacturer must require operators of aircraft of the same type and series to make replacements to the enhanced Brackets or take similar measures to prevent panels from departing the aircraft.
Effects of the Improper Bolts
Given that paint was not applied to the heads of the Improper Bolts only, it is probable that the bolts were mistakenly installed at the time of routine maintenance at the Operator. However, given that no marks indicating air flowed in behind the Panel assembly that was secured with the Improper Bolts were observed, and that the Improper Bolts were not used in other aircraft in which cracks in Brackets were found, it is probable that the possibility that use of the Improper Bolts was a direct factor in this serious incident is negligible.
Preventing Use of Improper Bolts
Depending on the Improper Bolts’ specifications and installation place, the attachment of similar panels using the Improper Bolts can be a direct factor in the similar panel’s departure. From the standpoint of preventing the occurrence of similar incidents, it is desirable that the Operator reviews its maintenance procedures (Compliance with the Maintenance Manual) and parts management and takes preventive measures concerning use of Improper Bolts so that the installation of Improper Bolts in aircraft does not occur.
Regarding the Site where the Panel Landed or Impacted
Given that the Panel arrived at the impact site at around 10:57, it is probable that, from the relationship with the Aircraft’s estimated flight route and times shown in Figure 1, the Panel likely departed from the Aircraft between points a and d and within a time period of about seven to ten minutes. Regarding the path the departed Panel took, this could not be clarified due to factors that include difficulty in estimating the precise point and time that the Panel departed from the Aircraft, the fact that the wind direction and wind speed were changing with the altitude along the Aircraft’s estimated flight route, the fact that the Panel was a thin plate that is easily influenced by the wind, and, further, the possibility that the Panel was blown by the wake turbulence of the Aircraft after it departed.
Aircraft Registration Data
This article is published under license from Avherald.com. © of text by Avherald.com.
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