On 1 November 2011, the crew of a Boeing 767-300 (SP-LPC) being operated by LOT Polish Airlines on an international passenger flight from Newark to Warsaw as LOT 16 were unable to extend the landing gear using either the alternate or free fall systems after the normal system had been disabled soon after takeoff due to a partial hydraulic system failure. After an ‘emergency’ had been declared, a daylight VMC approach was followed by a belly landing which resulted in the right engine catching fire. The aircraft was stopped on the runway and the engine fire was quickly controlled and a successful evacuation of all 231 occupants accomplished.
The aircraft in its final stopping position with evacuation beginning. [Reproduced from the Official Report]
An Investigation was carried out by the Polish State Commission on Aircraft Accidents Investigation (SCAAI). Data from the SSFDR, CVR and QAR were successfully downloaded.
It was found that the 57 year-old Captain, who had been PF for the accident flight, had 15,980 total flying hours which included 13,307 on type, most in command. He reported never having been faced with any emergency situations caused by technical failures in 22 years in command. The 51 year-old First Officer had 9,431 total flying hours which included 1,981 hours on type.
It was established that after takeoff from Newark, with the Captain as PF, the centre (main/C) hydraulic system had lost pressure due to leakage of its fluid during retraction of the landing gear and flaps. The crew had actioned the relevant procedure and noted that this failure would have prevented normal extension of the landing gear for landing. After consultation with LOT Maintenance Control, it was decided to continue to Warsaw as scheduled.
The aircraft track to its stopping point showing deviation right of centreline during deceleration. [Reproduced from the Official Report]
During the subsequent approach to Warsaw, two successive attempts to lower the landing gear using the Alternate Procedure were unsuccessful and an ‘Emergency’ was declared. Two checks that all CBs on the relevant CB panel were set were made by the First Officer who did not see any tripped CBs. Landing Gear deployment by free fall was also attempted but was also unsuccessful. Reducing fuel endurance eventually led the Captain to plan for a belly landing and this intention was communicated to ATC so that appropriate preparations could be made. These included the laying of foam over about 3,000 metres of the intended landing runway 33.
A 1.2g touchdown on the runway centreline with both engines operating was made at a groundspeed of 127 knots and a pitch attitude of +5.3°. After the right hand engine contacted the runway surface, it caught fire and the aircraft deviated to the right of the centreline before coming to a stop about two thirds of the way along the runway just after its intersection with runway 29. The fire in the right hand engine was a fuel-fed fire resulting of friction between the base of the nacelle and the runway surface and “intense sparking” was visible. On reaching the site, RFFS personnel signalled the flight crew to shut down both engines and were able to quickly extinguish the fire. It was subsequently estimated that approximately 1,600 kg of fuel had been left in tanks at touchdown.
The Captain had instructed the Senior Cabin Crew Member (SCCM) that an evacuation should commence as soon as the aircraft stopped without waiting for further orders, however in the event, the SCCM still sought confirmation from the flight crew before announcing this. Evacuation slides were deployed from doors 3L and 3R almost immediately but the same action at doors 1L/1R occurred 12 seconds later as a result of the SCCMs failure to heed the Captain’s prior instructions. The shallow angle of the rear slides slowed down their rate of use particularly when those assisting passengers to clear the bottom of the door 3R slide “ran away”. The dual over-wing emergency exits on the right side of the aircraft (2R1 and 2R2) were not used because of the engine fire on that side and although those on the left side of the aircraft (2L1, 2L2) were opened, these exits were not used either. All occupants were successfully evacuated with no injuries.
Rear emergency evacuation slides at a very shallow angle which reduced their rate of use. [Reproduced from the Official Report]
Damage to the aircraft was substantial and occurred to the lower aft part of the fuselage, both engines and their nacelles and to components of various on-board systems in the affected areas. It was subsequently classified as a hull loss.
It was noted that the Airport did not have the capability to remove such a large disabled aircraft from the runway and a significant delay ensued as the external contractor engaged to achieve this was based several hundred miles away from Warsaw.
The Alternate Gear Operation Failure
Visual inspection of the flight deck by investigators shortly after the accident found that the C829 BAT BUS DISTR circuit breaker situated at the inboard base of the P6-1 CB panel (see the illustration below) situated behind the Captain’s seat was tripped. An exhaustive examination and function testing of all systems and components whose malfunction could have caused the C829 CB to trip subsequently found no abnormalities and the CB itself was found to operate correctly. This 25 amp-rated CB controls the power to 13 subsidiary ones which then individually protect various emergency systems which included the 7½ amp rated CB protecting the Alternate Gear Extension Motor needed for Alternate or free fall gear extension to work.
In respect of how the C829 CB came to be tripped when alternate gear selection was attempted, it was considered that it was at least possible that it had for some reason already been tripped when the P6-1 panel had been checked by the First Officer during the Pre Flight Checks prior to departure from Newark but this had gone unnoticed given its floor level position. It was also considered feasible that the (routine) use of the space between the Captain’s seat and the P6-1 panel located behind it for stowage of such items as cleaning materials, shoes and crew baggage could have resulted in unintended tripping of this CB and that such use could also have obscured a tripped CB on the bottom row from detection by a less than thorough inspection, despite this being conducted in daylight.
The P6-1 CB Panel showing the C829 BAT BUS DISTR (annotated A1) and the C4248 LANDING GEAR-ALTN EXT MOTOR (annotated F6). [Reproduced from the Official Report]
It was noted that Boeing had been aware for some time that in-service experience indicated that because of its location, a protective guard over the P6-1 CB panel would be appropriate and in response had initially offered an SB to install one and then incorporated such guard at build. However, the accident aircraft had been manufactured prior to the modification being incorporated at build and LOT had not taken up the option to install the guard in accordance with the corresponding SB.
In terms of the support available to the flight crew once they found that they could not lower the gear using the alternate system, it was noted that they had been unable to make direct radio contact with Company engineering because of an inoperative ground radio and had been obliged to wait 20 minutes whilst an engineer drove to Operations Control. His advice had then not been informed by a full understanding of the way the alternate gear extension system worked or was controlled. The First Officer reported that he had, in response to the engineer’s advice “checked all of the circuit breakers on the P6-1 panel” and tripped and reset the C4248 CB. However, he reported that he had not tripped and reset the C829 CB nor had he been instructed to do so. It was noted that subsequent to this, the Captain had instructed the First Officer to re-check the same circuit breaker panel again “this time in the presence of the Chief Flight Attendant” and that the First Officer had subsequently reported to both the Captain and by radio to Operations Control that this had been done. The Captain stated that he had been focused on controlling the aircraft and had consequently “monitored FO actions only as far as he could from his position”.
The Hydraulic System Failure
The cause of the loss of hydraulic pressure in the Centre or ‘C’ System was found to have been the sudden loss of most of its fluid when a hose connecting the right main gear leg to the (main) ‘C’ hydraulic system failed due to fracturing of the metal band around the end of the hose. A detailed examination of the crack in this hose was undertaken using a scanning electron microscope and it was found that there had been a “possible stress relaxation of the hose material resulting in material creep” which it was considered could have been the result of kinking at a location which according to the hose manufacturer, is common “because the hose does not swivel and often gets kinked during installation”. It was also considered that signs of abrasion on the inner Kevlar lining of the pressure sleeving were “indicative of repeated hose flexing due to pressure changes during the operation of the landing gear” which “may also indicate that the hose had not been correctly aligned when installed”. It was noted that there had been no relevant findings during the most recent routine (6000 hour) zonal inspection covering the damaged hose in March 2011.
It was further noted that Boeing had determined that the inadequate life in service of the type of hose fitted to the accident aircraft due to fluid leaks was due to exceedence of the minimum hose bend radius as originally installed and, in June 2000, had released an SB which fixed this problem by substituting a redesigned bracket and swivel fitting but LOT had decided not to make this change.
It was concluded that the Causes of the accident were as follows:
- Failure of the hydraulic hose connecting the hydraulic system on the right leg of the main landing gear with the centre hydraulic system, which initiated the occurrence.
- The fact that the C829 BAT BUS DISTR circuit breaker which controlled the power supply circuit of the alternate landing gear extension system was tripped when the centre hydraulic system was inoperative.
- The flight crew’s failure to detect the tripped C829 circuit breaker prior to the approach to land after detecting that the landing gear could not be extended with the alternate system.
Four Contributory Factors were also identified as follows:
- Lack of guards protecting the circuit breakers on P6-1 panel against inadvertent mechanical opening which subsequent to the manufacture of the accident aircraft have been included as standard.
- The location of the C829 circuit breaker location on panel P6-1 (an extremely low position) had impeded observation of its setting and favoured its inadvertent mechanical opening.
- A lack of effective procedures at the Operator’s Operations Centre, which had impeded specialist support for the flight crew.
- The Operator’s failure to incorporate Service Bulletin 767-32-0162.
Nine Safety Recommendations were made at an early stage of the Investigation in an ‘Interim Statement’ detailing the progress of the Investigation and no more were made upon its completion. These earlier Recommendations and a summary of the responses of the recipients during the five years between their issue and the completion of the Final Report were as follows:
- that the Boeing Company should verify and modify the following checklists:
- HYDRAULIC SYSTEM PRESSURE (C only)
- HYDRAULIC SYSTEM PRESSURE (L and C)
- HYDRAULIC SYSTEM PRESSURE (R and C)
- GEAR DISAGREE
Boeing responded that it has reviewed these Checklists and provides its response to the recommendation that they be modified in response to the SCAAI’s specific recommendations following.
- that the Boeing Company should modify the above four checklists by adding a subsection that in case of failure in the landing gear alternate extension the flight crew should check C4248 LANDING GEAR - ALT EXT MOTOR and C829 BAT BUS DISTR circuit breakers.
Boeing responded that it does not agree that an additional subsection should be added to the current checklist. The QRH Non-Normal Checklists (NNC) are intended to give the crew direction based on a single failure of a specific function or system. The QRH is a compact reference manual, and combinations of all possible multiple failures of all systems are not included due to the complexity that would result. The checklist instructions advise that system controls are assumed in the normal configuration for the phase of flight before the start of the NNC. In the context of this event, normal configuration means that all relevant circuit breakers are in the proper (closed) position.
- that the Boeing Company should develop a checklist specifying flight crew actions in case of the total failure of the landing gear extension systems.
Boeing responded that it does not agree that a separate checklist should be added for an all-gear-up landing. Section 14 of the QRH contains the checklist to be used in the event that the landing gear position disagrees with the landing gear lever position. This checklist includes instructions to utilize the alternate system to lower the gear. If any gear down (green) light is still not illuminated, the checklist instructs the crew to plan to land on available gear, which includes the case where no gear is available. The Flight Crew Training Manual provides further guidance in the case of gear disagree combinations. One of these combinations is for all gear up (or partially extended); the guidance provided includes the expectation that the engines will contact the ground first and the instruction to utilise the rudder in order to maintain the runway centreline.
- that the Boeing Company should introduce a mandatory Service Bulletin providing for physical protection of the circuit breakers located in the areas of direct contact with shoes, equipment for cleaning, luggage etc., in which the breakers may be damaged or unintentionally set in the OFF positions. This applies to all B767 operators which have not added such a protection to aircraft manufactured prior to inclusion of such protection at build.
Boeing responded that it is currently in the process of creating a Service Bulletin that will provide instructions and a kit of parts to operators regarding adding circuit breaker guards consistent with those installed at build in later manufactured aircraft and anticipated that this Bulletin will become available to Operators in the first quarter of 2014.
- that LOT Polish Airlines should, taking into account the conclusions of the Commission, verify and modify the above cited checklists.
LOT Polish Airlines responded that they have partially implemented this recommendation. They have recommended that the ‘After gear down lights illuminate’ section of the ‘HYDRAULIC SYSTEM PRESSURE (C only)’ procedure should be removed and have introduced a ‘GEAR UP LANDING’ procedure which refers to the ‘GEAR DISAGREE procedure. In the ‘GEAR DISAGREE’ they propose to enter: ‘Any or all gear down (green) light not illuminated’. They advise that the gear up landing technique is described in FCTM and is known to their crews.
- that LOT Polish Airlines should modify the above four checklists by adding a subsection that in case of failure in the landing gear alternate extension the flight crew should check C4248 LANDING GEAR - ALT EXT MOTOR and C829 BUT BUS DISTR circuit breakers.
LOT Polish Airlines responded that they do not see sufficient grounds for the implementation of this Recommendation at this stage.
- that LOT Polish Airlines should develop a checklist specifying the flight crew actions in case of the total failure in the landing gear extension systems.
LOT Polish Airlines responded that they do not see sufficient grounds for the implementation of this Recommendation at this stage.
- that LOT Polish Airlines should, in consultation with the Boeing Company, install physical protection of the circuit breakers located in the areas of direct contact with shoes, equipment for cleaning, luggage etc., in which the breakers may be damaged or accidentally set in wrong positions. This applies to all Boeing 767 aircraft used by the operator which do not already have such a protection.
LOT Polish Airlines responded that on June 27, 2012, in the scope of the above Recommendation, the Company Continuing Airworthiness Management Office requested that Boeing develop a Service Bulletin to install a physical protection of the circuit breakers located in the areas of direct contact with shoes, equipment for cleaning, luggage etc. and that they were currently awaiting the outcome.
- that Warsaw Chopin Airport Management should develop procedures for the quick and smooth movement of passengers to a designated area or designated means of transport after evacuation.
Warsaw Chopin Airport Management responded that the aftermath of the accident had been analysed in detail and then discussed by services responsible for conducting and coordinating rescue and fire fighting operations at the airport in the context of regular training exercises. They noted that the Local Emergency Response Action Plan ensures coordination of activities related to flow of passengers from an occurrence site to the airport boundary and that since 23 September, the airport has had the ability to remove disabled aircraft of the Boeing 787 category.
The Final Report of the Investigation was completed on 5 May 2017 and subsequently published online in English translation on 15 December 2017.