Hevilift PNG DHC6 at Mount Hagen on Oct 18th 2020, hydraulic failure and smoke in cockpit during go around
Last Update: September 21, 2021 / 16:03:55 GMT/Zulu time
Papua New Guinea's Accident Investigation Commission (PNGAIC) reported the occurrence was rated a serious incident and is being investigated.
On Nov 18th 2020 the PNGAIC released their preliminary report describing the sequence of events:
The flight crew was composed of the pilot in command (PIC) as pilot flying, and the first officer (FO) as pilot monitoring.
During the arrival of the aircraft at Mount Hagen area, the air traffic services (ATS) instructed the flight crew to fly to Komon and join right base for approach and landing on runway 30. According to the information provided by the crew during their interview with the AIC, they maintained about 1,000 ft above ground level (AGL) during the track to Komon as they found low cloud and poor visibility along the approach.
As the approach progressed, and consistent with the information from the recordings of the air traffic control frequencies, when the crew reported that they were almost overhead runway 30 but had not sighted the references for landing, ATS therefore instructed the crew to perform a go-around.
The crew completed the go-around and upon rejoining the circuit pattern, a burning smell and subsequently smoke emanating from the floor area on the co-pilot’s side was identified by the flight crew. According to their statements, the FO open his side window and the PIC opened the vents and the smoke dissipated. The crew concurrently observed a series of alerts and fault messages related to the aircraft’s hydraulic system.
The crew stated that they observed cloud breaks and better visibility along the approach path of runway 12. Therefore, they requested for an approach and landing on runway 12, and for emergency services to be on standby.
ATS cleared the aircraft for a landing on runway 12, and the crew subsequently tracked for approach to runway 12 and landed.
In their interviews, the flight crew stated that due to the hydraulic failure, they decided not to use brakes during landing. Instead of brakes, they decided to use reverse thrust. They also stated that during landing, there was an indication of Hydraulic Low Pressure Warning, which was later confirmed by the AIC when analysing the Flight Data Recorder (FDR) data.
The flight crew also stated that landing was followed by a normal taxi to the parking bay where the aircraft parked and, after the shutdown checks, the FO exited the aircraft to secure the aircraft before normally disembarking the passengers.
On Sep 21st 2021 the PNGAIC released their final report concluding the probable causes were:
The investigation determined that the two consecutive abnormal and extended high hydraulic pressure cycles that were sustained in flight were due to the inconsistent operation of the pressure switch causing the relay switch to remain engaged and continue operating the hydraulic pump beyond its normal operation limit. The AIC observed no evidence that indicates that the relay failed in operation. The deformation observed on the relay contacts was determined to be pitting due to the arcing associated with such electromagnetic devices.
The investigation also determined that the continuous high demand on the hydraulic pump as a result of the intermittent failure of the pressure switch led to a Hyd Pump Over Temp Caution CAS message, due to heat being generated within the component’s housing. The extended operation of the hydraulic pump likely caused the significant wear of the bearings found during the examination. Additionally, a short was created in the hydraulic pump’s armature causing the hydraulic pump to fail and the Hydraulic Power Failure Warning to activate.
Even when the Manufacturer released an AOM directing operators to ensure their pilots action the Hydraulic Pump Over Temp abnormal procedure under specified conditions, the investigation determined that in the context of the occurrence, that procedure was not carried out by the crew. In addition, the investigation found that the Operator’s document control system did not effectively ensure that external documents and technical publications were distributed to the appropriate personnel and, in this particular case, the AOM was never brought to the knowledge of the pilots.
The lack of awareness about the AOM may have conditioned the decision made by the PIC to focus on an immediate safe landing rather than to action the checklist of respective hydraulic abnormality alerts that were received.
Additionally, the Operator’s QRH that was in use at the time of the occurrence was outdated and had incomplete procedures for hydraulic abnormalities available to the flight crew.
Subsequently, during final approach, when flap was extended to 20º, the System Pressure significantly dropped, and continued to drop and, after touchdown, during the landing roll, the Hydraulic Press Low Caution and Hydraulic Press Low Warning activated.
In addition, the investigation determined that the Operator did not have the necessary records to demonstrate that the rework of the hydraulic pump was done in accordance with the Viking Technical Bulletin TBV6/00031 before it was installed on the aircraft.
This article is published under license from Avherald.com. © of text by Avherald.com.
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