ASN Wikibase Occurrence # 244774
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| Date: | Sunday 18 October 2020 |
| Time: | 08:54 LT |
| Type: |  Viking Air DHC-6 Twin Otter 400 |
| Owner/operator: | Hevilift |
| Registration: | P2-KSY |
| MSN: | 875 |
| Fatalities: | Fatalities: 0 / Occupants: 16 |
| Aircraft damage: | None |
| Category: | Serious incident |
| Location: | Mount Hagen Airport, Western Highlands -
 Papua New Guinea
|
| Phase: | En route |
| Nature: | Passenger - Non-Scheduled/charter/Air Taxi |
| Departure airport: | Kairik |
| Mount Hagen | |
| Investigating agency: | AIC PNG |
| Confidence Rating: |  Accident investigation report completed and information captured |
On 18 October 2020, at about 08:54 local time the crew of a DHC-6-400 Twin Otter aircraft, registered P2-KSY, operated by Hevilift (PNG) Aviation Limited, identified the presence of smoke in the cockpit while overflying Mount Hagen Airport, following a discontinued approach to runway 30.
The aircraft was on an IFR passenger charter flight from Kairik, Enga Province. The pilot in command (PIC) was the designated pilot flying. The co-pilot was pilot monitoring.
According to the Flight Data Recorder (FDR) data, about 34 nm from Mt. Hagen, at 08:34:55, hydraulic pressure spiked up to 1,888 psi and remained above 1,575 psi for about 9 minutes. At 08:49:01, about 4nm from Mt. Hagen, the pressure spiked again up to 1,900 psi and remained above 1,575 psi for about 9 minutes. Information about hydraulic pressure is constantly available to the crew through the multifunction display unit (MFDU). However, there was no evidence that the crew noticed these abnormal parameters or that they reacted to them.
About 12 nm North West of Mount Hagen Airport, the crew established contact with Hagen Tower. The crew were instructed to track to the Komun area for an approach to runway 30 and were provided with weather and air traffic information. The aircraft established over Komun at about 08:53, at a height of 1,500 ft AGL2 (6,900 ft AMSL).
The crew stated that they subsequently turned the aircraft right for the approach, but they decided not to descend due to low cloud along the approach path. Instead, they continued tracking towards the runway at the same height. Just over 1 nm from the runway, the crew called Hagen Tower and reported that they did not have the runway in sight at that point. Hagen Tower subsequently instructed the crew to go around and track towards the Baiyer.
According to the FDR data, at 08:54:36, tracking to overfly the aerodrome, maintaining 1,500 ft AGL, the Crew Alerting System (CAS) Hydraulic Power Failure Warning message displayed on the MFDU along with the Master Warning4 activation. At that time, the actual hydraulic Brake Pressure was 1760 psi, and the System Pressure was about 1784 psi.
The crew stated that subsequent to receiving the hydraulic system related CAS alerts, they observed pressure readings on the MFDU indicating sufficient System Pressure and high Brake Pressure.
At 08:55:09, as the aircraft passed overhead the aerodrome, tracking North towards the Baiyer, the Hydraulic Pump Over Temp Caution activated along with the Master Caution.
The crew confirmed that the smoke smell in the cockpit continued to intensify, and the co-pilot recalled observing a thin wisp of smoke coming from the cockpit floor on the right side of the co-pilot’s yoke.
The co-pilot notified the PIC of the presence of smoke in the cockpit and proceeded to slide his window down while the PIC opened the vents allowing the smoke to disperse. At this time, the aircraft was tracking outbound towards the Baiyer area.
The PIC stated that he decided not to apply any abnormal or emergency procedure as the aircraft appeared stable, the MFDU hydraulic pressure readings showed that there was very high brake pressure and sufficient system pressure available, and also to avoid the use of the manual hand pump to maintain hydraulic pressure.
At 08:55:44, less than 1 nm North of the airfield, outbound towards the Baiyer area, the crew requested for an approach to runway 12, adding that they were experiencing an in-flight emergency. Hagen Tower instructed the crew to continue tracking towards the Baiyer and hold. The crew responded to Hagen Tower notifying them of a hydraulic problem with possible smoke and, again, requested to land on runway 12.
At 08:56:16, the crew reported to Hagen Tower that they were 2 nm from the field and requested to turn inbound and track for runway 12. The crew also requested for weather on runway 12. Hagen Tower subsequently instructed the crew to report when turning inbound and provided the weather for runway 12.
Following Hagen Tower’s clearance, at about 4 nm North West of the airfield, 1,300 ft AGL, the crew conducted a right turn and began tracking South West to intercept the approach path for runway 12.
The crew also commenced a shallow descent as they tracked towards the South West. The PIC stated during interview that they carried out the Final Approach checklist setting the aircraft flap to 20 degrees, propellers to maximum rpm and maintaining a final approach speed between 75-80 kt. The PIC briefed the co-pilot about the landing and use of reverse thrust.
FDR data showed that when the flight crew extended flaps to 20º during final approach, a rapid decrease in the hydraulic system pressure occurred.
At 09:00:20, about 300 ft AGL, the aircraft turned left, onto the final approach. According to the FDR data, the aircraft touched down at 09:00:57. The FDR data showed that the Hydraulic Press Low Caution was activated at 09:01:10 during the landing roll. Three seconds later, the Hydraulic Press Low Warning and the Master Warning activated. The data also showed that reverse thrust was applied during the landing roll.
After completing the landing roll, the crew used asymmetric power and nose wheel steering to taxi and exit via taxiway Bravo and to the parking bay, where engines were shut down and a normal disembarkation was conducted. The ARFFS team entered the runway from taxiway Alpha and escorted the aircraft from behind.
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.
Accident investigation:
 |
|
Sources:
PNG AIC
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 10-Nov-2020 07:52 | Petropavlovsk | Added |
| 19-Dec-2021 09:26 | harro | Updated [Time, Total fatalities, Total occupants, Location, Phase, Nature, Departure airport, Destination airport, Source, Damage, Narrative, Accident report] |
| 25-Jun-2023 11:02 | Ron Averes | Updated [[Time, Total fatalities, Total occupants, Location, Phase, Nature, Departure airport, Destination airport, Source, Damage, Narrative, Accident report]] |
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