Alliance F100 at Rockhampton on Nov 10th 2019, speed below minimum speed despite recovery attempts on landing

Last Update: June 7, 2022 / 17:12:06 GMT/Zulu time

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Incident Facts

Date of incident
Nov 10, 2019

Classification
Incident

Flight number
VA-1251

Aircraft Registration
VH-UQN

Aircraft Type
Fokker 100

ICAO Type Designator
F100

An Alliance Airlines Fokker 100 on behalf of Virgin Australia, registration VH-UQN performing flight VA-1251 from Brisbane,QL to Rockhampton,QL (Australia) with 97 passengers and 4 crew, was on final approach to Rockhampton's runway 33 when the aircraft encountered moderate turbulence at about 300 feet AGL, which caused the loss of airspeed. While attempting to arrest the loss of airspeed, the airspeed fell below the minimum approach speed because the flight crew failed to push the throttles forward. The aircraft managed a safe landing nonetheless.

The aircraft remained on the ground for about 12.5 hours before performing the return flight.

Australia's ATSB rated the occurrence an incident and opened an investigation. The Dutch Onderzoeksraad (Dutch Safety Board DSB) have joined the investigation.

On Jun 7th 2022 the ATSB released their final report concluding the probable causes of the incident were:

Contributing factors

- On final approach to land at Rockhampton Airport, reduced visibility and turbulence from a bushfire added uncertainty and late identification of a high approach profile.

- On final approach, the flight crew experienced a low airspeed management event.

- The operator’s training for the Fokker F28-Mk0100 did not prepare pilots for alpha mode activation during critical phases of flight. (Safety issue)

- The flight crew were unaware the alpha mode had activated, resulting in mode confusion prior to and after they advanced the thrust levers on final approach.

Other factors that increased risk

- On short final, the aircraft's rate of descent increased beyond the operator's stable approach criteria. The crew did not consider that the approach was unstable and continued the approach due to perceived blocked thrust levers, and possible adverse consequences of conducting a go-around.

- Changes in the operator's key safety post holder positions, safety reporting systems and internal processes reduced effective safety assurance. (Safety issue)

- The operator’s safety management reporting system did not enable the effective prioritisation of submitted safety reports. (Safety issue)

Other key findings

- Although the operator provided guidance to flight crews about the stable approach criteria, it did not specifically permit transient exceedances of the set criteria.

- Associated with a number of reasons, there was a significant delay in the occurrence (which was a routinely reportable matter) being reported to the ATSB.

The ATSB analysed:

Introduction

While on final approach to runway 33 at Rockhampton Airport, the aircraft became slightly high on approach. Attempted corrections by the first officer (FO) to regain the approach path resulted in the aircraft entering a low speed/low thrust configuration, which activated the alpha mode protection. In response, the flight crew attempted to increase thrust, but the thrust levers appeared to be ‘blocked’. The FO forcibly moved the thrust levers and the aircraft was subsequently landed safely.

A post-flight engineering assessment found no evidence to indicate a technical problem, or failure of any of the mechanical components in the system, which may have led to the blocked thrust levers or inadvertent activation of alpha mode.

This analysis will consider the circumstances that preceded the incident, including weather, visibility, flight crew training, and stability of the approach. Changes to key safety management reporting systems and safety personnel, as well as post-incident circumstances such as organisational delays and the management of safety reporting, will also be discussed.

High approach profile

On the day of the incident, the southern Queensland aviation network was affected by widespread reductions in visibility due to bushfire generated smoke haze. Additionally, the Rockhampton area was impacted by moderate, low-level, convective turbulence from localised bushfires.

During descent at night into the strengthening north-westerly wind, the aircraft was buffeted by rising hot air and encountered smoke from the bushfires close to Rockhampton Airport.

Convective turbulence from rising and sinking air affected the aircraft’s vertical speed on the approach. Reduced visibility was encountered on final approach as smoke discoloured the runway lighting and precision approach path indicators (PAPI), rendering the vertical approach guidance lights temporarily unusable.

During the late stages of the approach, the flight crew reported that, at about 400 ft, the smoke discolouration of the PAPI lights reduced and they identified that they were slightly high on the approach profile. The aircraft’s airspeed and vertical approach profile was affected by convective turbulence from a local bushfire, impacting the flight crew’s ability to maintain the approach path.

The FO reduced the thrust setting and lowered the nose of the aircraft to correct for being slightly high on the approach path. This, coupled with convective turbulence, very likely resulted in an increased rate of descent and subsequent airspeed reduction towards the minimum approach speed (VMA).

High descent rate

Flight crew reaction to changing in-flight performance, requires them to identify a parameter change is occurring, decide to apply correction, apply the correction technique, monitor the correction for change against the parameter, identify that the desired parameter has been regained, reduce corrective input, and monitor for change.

The aircraft’s flight data noted 2 high rate of descent events when below 600 ft on approach, with a maximum rate of about 1,200 ft/min for a short period of time. This exceeded the operator’s stable approach criteria, which required a rate of less than 1,000 ft/min. The identification of the high descent rate may not have been as immediate as the data suggested, as the flight crew were in the higher workload phase of landing in challenging conditions. Granularity of the vertical speed indicator increments, abbreviated vertical speed readout and display layout most likely affected the flight crew’s ability to readily identify the increased rate of descent above 1,000 ft/min. This required greater attentional resources to identify, correct and monitor the rate than the flight crew had available with the late PAPI identification (as the smoke cleared) of the slightly high approach profile while entering convective turbulence.

Low airspeed management

While on final approach, the FO overrode the autothrottle system, manually reduced the thrust setting and lowered the nose of the aircraft to correct for being slightly high on the approach path.

This, combined with the convective turbulence from the bushfire, resulted in a fluctuating rate of descent, peaking at about 1,200 ft/min for about 6 seconds. The recorded flight data showed that the airspeed decreased below the minimum approach speed (VMA). As a result of the low speed, low thrust condition, alpha mode activated at 203 ft.

Consequently, after the captain’s second ‘speed’ call, the FO had to forcibly move the thrust levers forward to counteract the thrust lever resistance, as a result of alpha mode activation. The alpha mode activation combined with flight crew’s actions resulted in the aircraft responding to the increased thrust.

The airspeed increased above the VMA about 3 seconds after alpha mode activated. Alpha mode then disengaged, allowing free movement of the thrust levers, which may explain why the FO described experiencing a reduction in thrust lever resistance. While the airspeed reduced to 5 kt below VMA for 1 second, the airspeed remained above the stall speed by about 27 kt before recovering, and a normal landing made.

Mode confusion

During the approach to land, both pilots identified the deceasing airspeed and attempted to rectify this. However, neither recognised that alpha mode had activated. The FO had identified that the thrust levers appeared blocked, but could not identify why this occurred. Consequently, they continued to force the thrust levers forward, without knowing that the alpha mode system was actively increasing thrust to recover airspeed. The flight crew continued the approach, and considered that the conduct of a go-around may place the aircraft in a nose high, slow speed condition without the sufficient thrust, thereby increasing the risk of loss of control.

After an uneventful landing, the flight crew discounted the possibility of an alpha mode activation as they recalled that the airspeed had not reduced below the minimum approach speed. Mode awareness is a type of situational awareness based on the pilot’s understanding of aircraft configuration and flight control system modes. Being aware of the active mode(s) and understanding the corresponding actions and responses is necessary for proper use of the autoflight system. Ineffective auto-flight system mode awareness has been identified as a contributing factor in many occurrences since the introduction of complex auto-flight systems (United States Federal Aviation Administration, 1996).

Flight crew training on alpha mode

As per the operator’s standard practice, the flight crew had been checked as competent on their understanding of alpha mode during their initial aircraft type training. However, the simulator demonstration was conducted at altitude and did not include elements of competency relating to alpha mode activation in different flight configurations and states, or at critical times such as final approach. Further, the training did not include the higher force caused by the dynamic rod lockout, which was only applicable to the operator’s F100 fleet. The operator’s flight crew may operate both variants at different times.

In addition to the initial training, flight crews were not routinely assessed on alpha mode during cyclic training. Recurrent or cyclic training was a mechanism for developing and assessing flight crew performance across a range of necessary competencies. This ensured that each crew member was adequately trained and proficient for the aircraft type and their position held. As highlighted by the Civil Aviation Safety Authority, recurrent or cyclic training assists with the prevention of the degradation of critical skills over time.

In this case, it had been more than 1–2 years since the flight crew had completed their initial type training for the F100, noting that this did not capture all aspects regarding alpha mode. As such, the flight crew were not aware that alpha mode activation could occur above the minimum approach speed in different aircraft states or that thrust lever resistance would be experienced when in this mode. Therefore, the initial type qualification training on the F100 did not adequately prepare pilots to recognise and recover from an alpha mode activation during a critical phase of flight, such as during approach to land. Also, there was no further cyclic training in relation to alpha mode activation and procedures to support flight crew decision making when such an activation occurred.

Stabilised approach criteria

The operator’s criteria for stabilised approach was reviewed and found to be consistent with the International Civil Aviation Organization (ICAO) recognised standard operating procedures. The operator provided this information to flight crew by publication in the Operations Policy and Procedures Manual – Standard operating procedures.

The review of other operators’ manuals found that their procedures allowed for momentary exceedances of the stabilised approach criteria. This allowed flight crew to continue an approach with some flexibility to external environmental influences. The operator’s published stabilised approach criteria did not reflect this flexibility, and the operator’s internal investigation did not consider the approach to be unstable and no further mention of the stabilised approach criteria was identified.

New safety reporting system

The operator’s newly introduced safety reporting system displayed submitted reports on a dashboard in date and time order, and assigned a visual coloured 72-hour countdown timer to aid in tracking. This visual tool was displayed against all submitted reports, not just those required to be notified to the ATSB. However, due to the design of the system, ATSB notifiable reports that were submitted late would not only have appeared further down the list, but appeared overdue.

Similarly, other occurrences that did not require reporting to the ATSB, however required validation by the relevant department responsible managers, would have also appeared overdue.

As previously mentioned, safety reporting systems are an essential tool within a safety management system for gathering valuable safety information. This information could be used for identifying occurrences that required further investigation, for discovering lessons learnt, and for providing a useful source of information for hazard identification. However, this was reliant on a system design that was effective.

In this case, when the captain’s safety report was submitted about 2 days after the incident, it was not likely displayed on the initial dashboard screen due to the date order and it would have been listed below already overdue reports. This meant that it would not have been clearly visible to the safety department staff. This system characteristic was not identified prior to this incident, which made identification and subsequent report tracking more difficult for the safety department. In turn, this did not allow for the effective prioritisation of submitted safety reports.

Organisational change

There had been a significant turnover of staff within the operator’s safety department prior to the incident, with a number of key staff having only been in their respective positions for less than 6 months. This coincided with the introduction of the new safety reporting system. This reduced short-term organisational memory relating to the introduction of the new system, and came at an important stage of system implementation, with the redevelopment of new supporting processes under the operator’s standard operating procedures. This required increased education to the operator’s staff on the use of the new system, by the safety systems department. This likely affected the safety systems manager (SSM) and the acting SSM (ASSM), with increased tasks and workload during a period of organisational and role assimilation within the operator.

The ASSM was approved as the alternate postholder position for the SSM. However, having not previously acted in the role, and with a limited handover, it was unlikely that the ASSM was able to adequately fulfill the requirements of this role in addition to their ordinary workload and remote duties.

Implementation of supporting processes into the operator’s standard operating procedures for the new safety reporting system relied on the SSM to review and make changes to the existing organisational process. However, all procedures had not yet been finalised, in particular, that relating to further requests for information for immediately and routine reportable matters to the ATSB. Therefore, there was little guidance available to the ASSM regarding ATSB reporting.

Safety assurance is a key component of a safety management system. Of particular importance are changes to internal systems and processes or procedures. As previously highlighted by the International Civil Aviation Organization, such changes could inadvertently introduce new hazards and associated risks to an operation. The system change, coupled with new employees in the safety department, and the redevelopment of internal processes, did not identify the visual display deficiencies and possible unintended outcomes of the new safety reporting system. This increased the safety department’s workload and introduced an increased risk of some reports not being appropriately classified, reported, or acted upon in a timely manner.
Aircraft Registration Data
Registration mark
VH-UQN
Country of Registration
Australia
Date of Registration
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Airworthyness Category
TCDS Ident. No.
Manufacturer
FOKKER AIRCRAFT B.V.
Aircraft Model / Type
F28MK0100
ICAO Aircraft Type
F28
Year of Manufacture
Serial Number
Maximum Take off Mass (MTOM) [kg]
Engine Count
Engine
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Main Owner
Qdglinefnhbekikpmbqh lbjpdj fcAfecdAmikidpkgckjpkbdhqjjpdpdpcnnelq lgAp ikhAmhkAdnncgkfAmm lepgflhqk Subscribe to unlock
Main Operator
AAlqppd pjpdimgiiempqjldpgqlgl j qnAcijilAhmgbnhejblkiillcinlcAedc h dfinhfi gkimihAmphpllkmmknnhpegAjkf Subscribe to unlock
Incident Facts

Date of incident
Nov 10, 2019

Classification
Incident

Flight number
VA-1251

Aircraft Registration
VH-UQN

Aircraft Type
Fokker 100

ICAO Type Designator
F100

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