Virgin Australia B738 at Apia on Apr 23rd 2016, pod strike on landing
Last Update: June 30, 2020 / 15:01:41 GMT/Zulu time
Incident Facts
Date of incident
Apr 23, 2016
Classification
Incident
Airline
Virgin Australia
Flight number
VA-91
Departure
Auckland, New Zealand
Destination
Apia, Samoa
Aircraft Registration
VH-YIW
Aircraft Type
Boeing 737-800
ICAO Type Designator
B738
Airport ICAO Code
NSFA
The aircraft was unable to depart for the return flight, the return flight VA-92 was cancelled.
The occurrence aircraft departed Apia for a positioning flight VA-9552 to Auckland about 21 hours after landing and resumed service. However, on Apr 26th 2016 the aircraft was removed from service after landing in Brisbane,QL (Australia) and is on the ground in Brisbane since (for 8 days so far). This move was the result of a routine review of the flight data, which identified not just a firm arrival in Apia, but the possibility of an engine (CFM56) pod strike prompting an additional inspection, which identified a pod strike had indeed occurred.
The Australian Transportation Safety Board (ATSB) reported, that the occurrence was rated a serious incident, an investigation has been opened. The ATSB stated: "During the final approach and landing at Foleolo International Airport, the weather conditions consisted of heavy rain and gusting winds. The crew reported touching down firmly, making first contact on the right main gear. A subsequent, routine flight data review by Virgin Australia on 26 April 2016 identified that a firm landing had taken place, consistent with the landing at Apia. The aircraft was inspected and a pod strike was identified on the No. 2 (right) engine. The ATSB was notified of the hard landing on 26 April 2016 and initiated an investigation."
On Jun 30th 2020 the ATSB released their final report concluding the probable causes of the serious incident were:
Contributing factors
- The aircraft drifted left during short final in heavy rain on an approach at night. The pilot flying started to correct the drift, however the aircraft was not flared and the wings were not level as it touched down. This led to the nose and right wing being low, resulting in an engine nacelle strike.
- Due to heavy rain, darkness and limited visual cues, the flight crew did not detect the aircraft's banked, nose-low attitude immediately prior to landing which increased the likelihood of an engine nacelle strike.
- The operator’s pre-flight external inspection procedure mandated that flight crew check under the engine nacelle for damage. This was not routinely done by flight crew and not included in the flight crew training material.
- Although the operator had a maintenance task card for daily inspections of the Boeing 737, it did not contain a specific requirement to inspect underneath the engine nacelle. This contributed to the damage to the right engine nacelle not being identified during in postoccurrence maintenance inspections.
Other factors that increased risk
- Due to limited sleep in the previous 24 hours, the captain was probably experiencing a level of fatigue that has been demonstrated to adversely influence performance.
The ATSB analysed:
The flight departed Auckland with an approaching tropical cyclone in the vicinity of Apia. At the time of departure, the effects of the tropical cyclone where not expected to adversely impact the safety of the flight.
The approach to land was conducted within the aircraft’s operational limitations at night and in heavy rain. During the touch down, the right engine nacelle momentarily contacted the runway.
Damage from the runway contact to the engine nacelle was not detected after landing or during any of the pre-flight and engineering inspections for four subsequent sectors.
...
TC Advisory No. 13 was not provided to the flight crew prior to departure or during the flight. The operator’s flight following service was in receipt of Advisory No. 13, which was available if requested by the crew.
However, the updated information contained in Advisory No. 13 did not contain any significant change from the previous forecast and was not deemed by flight following to contain operationally critical information and therefore was not actively provided to the flight crew. The flight crew utilised requested aerodrome forecasts and observed weather reports from Apia air traffic control to prepare the aircraft for landing in Samoa.
...
Sleep is vital for recovery from fatigue, with both the quantity and quality of sleep being important. Most people need at least 7–8 hours of sleep each day to achieve maximum levels of alertness and performance. Research has shown that obtaining less than 5 hours’ sleep in the previous 24 hours is inconsistent with a safe system of work (Dawson and McCulloch 2005), with some research indicating less than 6 hours sleep can increase risk (Thomas and Ferguson 2010, Williamson and others 2011). In addition to sleep, a number of other factors can influence fatigue levels, including time of day, time awake and the nature of work activities.
In this case, the captain reported having 3–4 hours’ sleep the night before the occurrence flight, and he had been awake for 13 hours at the time of the engine nacelle strike occurrence. He also stated that he did not feel fatigued, but most people generally underestimate their level of fatigue (Battelle Memorial Institute 1998). The first officer had significantly more sleep prior to the occurrence flight.
Overall, primarily due to restricted sleep in the previous 24 hours, it is likely the captain was experiencing a level of fatigue during the occurrence flight likely to have a demonstrated effect on performance. However, there was insufficient evidence to conclude he was experiencing a significant level of fatigue. In addition, it is difficult to conclude that the captain’s performance during the landing was influenced by fatigue. Other factors, such as reduced visual cues and environmental conditions, can explain the handling events, and the environmental conditions and context during the approach is likely to have elevated the crew’s arousal level.
The occurrence at Apia occurred during the first of two flights scheduled for the flight crew that day. Had the duty period proceeded as planned, it is likely that both flight crew would have been experiencing a higher level of fatigue towards the end of the second flight. However, both flight crew may have been able to enhance their alertness during that flight by taking controlled rest.
Overall, the flight crew’s scheduled flights on 23 April met the requirements of the operator’s fatigue risk management system. Nevertheless, this occurrence highlights the importance of ensuring that both flight crew and an operator adequately consider a flight crew member’s circumstances before extending duty periods.
...
Neither pilot reported the workload during the approach as being too high to manage. They briefed for the approach and were actively monitoring the weather conditions, and they addressed the increased requirements for radar scanning successfully. However, final approach is normally known as a period of high workload for pilots, particularly at night. In this case, the workload was further increased by the changing weather conditions. The difficulty in communications with the tower, the crosswind, manual control of the aircraft and the potential influence of fatigue also added to this workload.
When the captain mistakenly selected take-off/go-around (TOGA) from the throttle controls instead of auto thrust disconnect, it had the effect of removing the flight director. This momentarily left the flight crew without a simple representation of pitch and bank angle guidance. With reduced visual cues due to the night-time conditions, rain and increasing crosswind on touchdown, the last 100 ft of the approach likely required the crew’s full attention to deal with the situation. Although the flight crew’s workload was undoubtedly higher than normal, the available evidence is not consistent with it being beyond the crew’s capabilities, and it is not possible to conclude that their elevated workload reduced their handling of the aircraft or their subsequent awareness of a nacelle strike.
The flight crew were aware that the landing had been non-standard and, after discussion with the captain, the FO obtained recorded data from the maintenance section of the on-board flight management computer. The FO’s interpretation of the data indicated that the landing had been conducted within normal parameters.
During the post-event investigation, the operator found that flight crew were not specifically instructed on how to interpret this data. Consequently, the FO did not understand the limitations in how the data was displayed, which led the flight crew to believe the landing was within acceptable limits, and alleviated any concerns they may have had with the landing. As a result, the flight crew did not alert the maintenance engineer of an increased likelihood of a hard landing or possible runway contact with the airframe.
With respect to the damage detection the ATSB analysed:
Flight crew conduct an external inspection of the aircraft before every flight. As part of these inspections, the engines and surroundings are required to be examined. This includes an explicit requirement to inspect the underside of the nacelles for damage. This requirement was added to the operator’s procedures in 2011, adding to a previous requirement in 2005 to check that the engine exterior was not damaged.
At the time of the occurrence, however, the operator’s flight crew training package did not reflect the specific requirement to check for this damage. The captain conducted the planned return sector pre-flight inspection at night, in heavy rain and wind. Although the environmental conditions were not optimal, the captain considered the inspection to be adequate. However, the flight did not proceed due to the weather and departed the next day, after an additional pre-flight inspection, when conditions had eased. No flight crew inspections for the next four flights were effective in detecting the nacelle damage. Consistent with other occurrences investigated by the ATSB, this may have been influenced by an expectation that no damage was present. The operator has since amended its pilot training package to include the specific requirement to inspect the underside of the engine nacelles.
Additionally, a licensed engineer was required to conduct an external inspection before the first flight of a day and conduct a separate external inspection using a different inspection schedule before an aircraft conducted an extended range twin-engine operations (ETOPS) flight. Neither the daily external inspection, nor the ETOPS external inspection specifically required the underside of the nacelle to be visually inspected. Engineers were required to carry out a visual check of various components for ‘obvious signs of damage’. This included the inlet cowl outer surfaces and the abradable shroud.
While the lower surfaces of the nacelle were not specifically mentioned, the inspection requirements were broad in their requirements and not specific in their intent. This may have led to engineers not specifically inspecting under the engine nacelles. Since the occurrence, a specific requirement to inspect the nacelles’ underside has been added to engineers’ procedures. A combination of rain, wind, and the position of the damage provided significant environmental challenges during the visual inspection.
Due to the positioning of the engines on a B737, the space between the underside of the nacelle and the ground is between 470 mm and 600 mm high, depending on the aircraft weight. While it is easy to inspect and access the sides of the nacelles, examining the underneath is more difficult.
Tests by the operator showed that even when crouching down to view the underside of the nacelle from 2 m away, the area of damage was not visible. This meant anyone examining underneath the nacelle would have to be positioned close to the ground to obtain an adequate view of the area and any potential damage. No additional equipment, such as mirrors or waterproof clothing, were issued to flight crew to facilitate this level of inspection.
Metars:
NSFA 231100Z 15010G22KT 2000 SHRA FEW013CB SCT016 SCT030 OVC100 25/24 Q1001
NSFA 230900Z 11023G37KT 2000 +SHRA SCT015 BKN030 OVC100 25/24 Q1002
NSFA 230822Z 11021G32KT 4000 +RA SCT015 BKN030 OVC100 25/23 Q1003
NSFA 230800Z 11020G27KT 6000 SHRA SCT014 BKN030 OVC100 25/24 Q1003
NSFA 230745Z COR 10023KT 4000 +RA SCT014 BKN030 OVC100 25/24 Q1003
NSFA 230700Z 09022G32KT 6000 RA SCT017 BKN034 OVC100 26/25 Q1004
NSFA 230645Z 09020G27KT 8000 RA SCT017 BKN034 OVC100 26/25 Q1004 POOR VIS
NSFA 230600Z 09015KT 9999 +DZ SCT018 SCT037 OVC110 26/24 Q1004
NSFA 230500Z 09017KT 9999 DZ SCT019 BKN038 OVC110 25/24 Q1003
NSFA 230400Z 09012KT 9999 SCT020 SCT038 OVC130 25/24 Q1004
Aircraft Registration Data
Incident Facts
Date of incident
Apr 23, 2016
Classification
Incident
Airline
Virgin Australia
Flight number
VA-91
Departure
Auckland, New Zealand
Destination
Apia, Samoa
Aircraft Registration
VH-YIW
Aircraft Type
Boeing 737-800
ICAO Type Designator
B738
Airport ICAO Code
NSFA
This article is published under license from Avherald.com. © of text by Avherald.com.
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