LOT B763 at Warsaw on Nov 1st 2011, forced gear up landing

Last Update: December 18, 2017 / 14:27:42 GMT/Zulu time

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Incident Facts

Date of incident
Nov 1, 2011


Aircraft Type
Boeing 767-300

ICAO Type Designator

On Dec 15th 2017 the Polish PKBWL released their final report in Polish. As all communication had also been available in English so far The Aviation Herald transmitted an according inquiry whether an English version of that report would be available, too, which resulted in a favourable reply by the PKBWL on Dec 18th 2017, who uploaded the English version on Dec 18th 2017 as result, too.

On Dec 18th 2017 the PKBWL released their final report concluding the probable causes of the accident were:

Failure of the hydraulic hose connecting the hydraulic system on the right leg of the main landing gear with the center hydraulic system, which initiated the occurrence.

2. Open C829 BAT BUS DISTR circuit breaker in the power supply circuit of the alternate landing gear extension system in the situation when the center hydraulic system was inoperative.

3. The crew’s failure to detect the open C829 circuit breaker during approach to landing, after detecting that the landing gear could not be extended with the alternate system.

Factors contributing to the occurrence were as follow:

1. Lack of guards protecting the circuit breakers on P6-1 panel against inadvertent mechanical opening; from 863 production line the guards have been mounted in the manufacturing process (SP-LPC was 659 production line).

2. C829 location on panel P6-1 (extremely low position), impeding observation of its setting and favoring its inadvertent mechanical opening.

3. Lack of effective procedures at the Operator’s Operations Centre, which impeded specialist support for the crew.

4. Operator’s failure to incorporate Service Bulletin 767-32-0162.

The PKBWL analysed:

Upon arrival of the SCAAI Investigation Team at the scene initial inspection of the cockpit and the passenger cabin was carried out. It was done by the Investigation Team member in the presence of a policeman and the Captain. During the inspection it was found that in the cockpit, on P6-1 panel the C829 circuit breaker on A1 position was in the OFF setting (pulled out). A circuit breaker in OFF setting has a visible white shaft which enables identification of the setting (Figure 25, description in section 1.6.4.).

A circuit breaker in OFF setting should be marked by ground engineers, and if not, it is abnormal situation and a reason/cause of OFF setting should be determined.

Due to the above the airplane documentation was analyzed to determine the role of C829 circuit breaker. Documentation showed that C829 protected 13 circuits including the alternate landing gear extension system. OFF setting of the circuit breaker caused, among others, that the actuator of the alternate landing gear extension system could not be powered when needed (normal extension of the landing gear was not possible due to failure of the center hydraulic system).

After confirmation that C829 circuit breaker protects the alternate landing gear extension system the Investigation Team decided to extend the landing gear using this system. After execution of the applicable procedure the landing gear was extended and locked.

The successful extension of the landing gear with the alternate system showed that all components of that system were operative (even after the emergency landing) and that the cause of the failure to extend the landing gear during LO 16 flight was open C829 circuit breaker.

The PKBWL analysed that two possible scenarios could have led to the triggering of the circuit breaker: a technical malfunction drawing sufficient current to trip the circuit breaker or human factors that led to the (inadvertent or intentional) trigger of the circuit breaker.

In reviewing all possible scenarios of how a technical overload of the circuit breaker could have happened, the investigation found all equipment depending on the circuit breaker to be technically fit, undamaged and not having caused the circuit breaker to trip. The investigation wrote: "All of the above described analyzes, checks and tests confirmed that all tested components of the alternate landing gear extension system were mechanically and electrically fit and that no electric overloads occurred, which could cause C829 circuit breaker to trip."

The investigation therefore proceeded to review possible human factors. The investigation was not able to determine the time at which the circuit breaker opened, the status of the CB was not recorded on the FDR and did not trigger any warning. It was only possible to determine that the CB had already been OFF prior to shut down of the engines following the gear up landing. The investigation wrote: "the Investigation Team concluded that C829 circuit breaker had been open prior to the attempt to extend the landing gear that took place during the approach to landing on EPWA."

Based on prior analysis the investigation analysed:

it may be presumed that the C829 circuit breaker was inadvertently opened in a time between the Pre-Flight Check in Newark and the attempt to extend the landing gear during the approach to landing in Warsaw.

Such a scenario is supported by the following facts and factors:

a) the location of C829 circuit breaker contributed to the physical contact of its head with objects placed in its immediate vicinity;

b) in the past, some operators contacted Boeing due to concerns about circuit breakers on P6 panels which were located in the vicinity of feet, cleaning equipment, flight bags, etc., and accidental openings or damage occurred.

Therefore, Boeing developed a “guard” to protect circuit breakers located in the lower parts of the panel. Boeing offered the guard on a charged basis;

c) Boeing started to install the guard in the production process starting from the 863 production line (SP-LPC was 659 production line).

The above facts indicate that Boeing 767s had problems with proper protection of the P6 panel which were noticed by operators and reported to the manufacturer. The manufacturer responded to those concerns and first offered the guard on a charged basis and then introduced it into manufacturing process.

The guards for the circuit breakers on the P6 panel were not installed on SP-LPC airplane.

The investigation analysed that they could neither establish nor rule out that the crew inadvertently triggered the CB during the flight from Newark to Warsaw.

The investigation further analysed that it was possible that even a pre flight check could have missed the tripped circuit breaker, as there was no indication, no recording and no warning. The investigation thus wrote: "the Commission stated that it was impossible to determine when and under what circumstances the C829 circuit breaker was set OFF/tripped."

The PKBWL analysed that none of the checklists, not the hydraulic failure checklist nor the checklist for a not functioning alternate gear extension, included a reference to the circuit breaker C829. The operations center, despite engaging experts, could not provide effective assistance to the crew. The operations center had recommended to the crew to continue the flight to Warsaw after the crew contacted dispatch following the hydraulic failure from Newark.

The PKWBL wrote:

The SCAAI Investigation Team determined that after analysis of the information from the crew received via ACARS, MCC did not consider a need of expert support to the crew during the flight. As a result, when the crew requested consultation with a ground engineer and an instructor pilot of B767, only then the process of searching for the right persons commenced.

A few minutes after the request the SP-LPC crew was contacted with an instructor pilot of B767, but contact with a ground engineer was possible only after about 20 minutes, since the ground radio station designated for this purpose was faulty and the ground engineer had to drive to the Operations Centre. Use of a nearest radio station was impossible due to restrictions on access to its location.

The Investigation Team determined that the Operator’s Operations Centre did not have a risk assessment system and anticipation of emergency situation escalation, what contributed to the time deficit, which was a key factor for successful solution of the emergency situation.

Analysis of the Operations Centre actions in the investigated occurrence did not entitle the Commission to conclude that the applicable rules or procedures were breached.

However, the Commission concluded that situation in which contact of the ground engineer with the crew was impossible due to failure of the radio which was intended solely for this purpose, was a serious negligence. The alternative was driving to the Operations Centre.
Incident Facts

Date of incident
Nov 1, 2011


Aircraft Type
Boeing 767-300

ICAO Type Designator

This article is published under license from Avherald.com. © of text by Avherald.com.
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