Description

On 8 November 2022, a De Havilland Canada DHC8-200 (VH-TQS) being operated by QantasLink on a scheduled passenger service from Lord Howe Island to Sydney experienced a radio altimeter failure during descent into Sydney which was followed by TCAS and EGPWS failure annunciations. On landing in day VMC, the engines unexpectedly reverted to manual control when reverse pitch was selected and the power levers were returned to flight idle which meant more braking was required. The brakes then failed as the allocated gate was approached and, once stopped, they were reported to be on fire and an emergency evacuation was ordered. The fire was put out by the airport RFFS and there were no injuries as a result of the evacuation.

Investigation

An Investigation into the event was carried out by the Australian Transport Safety Bureau (ATSB). The FDR and CVR were removed from the aircraft and their data were successfully downloaded. Relevant ADS-B data was also obtained from FlightRadar24. It was noted that the Captain, who was acting as PM, had “about 5,000 hours” flying experience which included 2,272 hours on type and the PF First Officer had “about 2,400 hours” flying experience which included 1,734 hours on type. 

What Happened

As the aircraft descended through FL 175, failure of both the TCAS and EGPWS systems was annunciated and the crew subsequently noticed that the radio altimeter had also failed. ATC were informed of the TCAS failure and the Captain consulted the QRH in respect of all three failures. A visual approach to runway 34R was flown but after touchdown, the First Officer’s routine selection of the propeller pitch into reverse (beta) range resulted in activation of the beta lockout warning horn and the power levers were returned to the Flight Idle position. The Captain then routinely took over control, as the aircraft was not fitted with a steering tiller at the right seat pilot position.

As they exited the runway, the pilots then reported noticing that the EGPWS and TCAS fault indications had disappeared but also that both engines’ manual caution lights were illuminated, indicating that their EECs, which automatically control the under-speed governing of the propellers during ground operations, were now in manual mode. They recognised that this required that the power levers must therefore remain at or above flight idle to ensure that the prohibited propeller speed range in beta mode was avoided.

The First Officer consulted the QRH Checklist for the engine caution lights and noted that it was presented for only a single light on rather than both on at the same time. After taxiing for almost 2 nm, (see the illustration below) the aircraft reached the B8 holding point, the limit of their taxi clearance, and stopped the aircraft. Whilst stopped, company engineering support were contacted about the dual engine manual control status but had no instant advice to offer.

When further clearance was given, taxi was resumed on a slightly downhill slope and when braking the Captain reported having noticed that the response to his brake pedal inputs was reducing. By the time the allocated terminal parking position was approached - after about 3 nm of taxiing - there was no braking response at all and the Captain turned the aircraft onto their allocated gate and stopped using the parking brake. At this time, the cabin crew called on the interphone to report that fire in the vicinity of the main landing gear was visible from mid cabin on both sides of the aircraft. An emergency evacuation was ordered and commenced and the First Officer exited the aircraft with a BCF fire extinguisher and attempted unsuccessfully to extinguish the fires. A short time later, the airport RFFS arrived and quickly extinguished both fires using foam fire retardant. 

The aircraft track after touchdown annotated with the position at significant points. [Reproduced from the Official Report]

Why It Happened

The QRH did not include any reference to the consequences of a radio altimeter failure or reference the consequences of such a failure on other systems. It also did not contain any information on the specific consequences of an airborne radio altimeter failure on the electronic engine control system once on the ground or reference the fact that loss of the EEC may affect both engines simultaneously. Although the crew responded to the indicated EEC loss correctly by keeping the propellers out of the beta range, they evidently did not recognise that the significantly greater brake use consequently required over an unusually long taxi distance would probably overheat the brakes.

It was also noted that despite the inclusion of a restriction on BCF extinguisher use to in-flight fires during their annual emergency training, neither pilot seemed to be aware that the Aircrew Emergency Procedures Manual stated clearly that the use of BCF (Bromo Chloro di-Fluoromethane) extinguishers on high temperature metal fires such as a brake fire on the DHC-8-200 can result in the generation of toxic fumes.

Four Contributing Factors were formally documented based on the Findings of the Investigation as follows:

• The radio altimeter failure led to the beta lockout system relying solely on the weight on wheels to prevent the activation of the beta lockout system.
• During the touchdown, in accordance with standard operating procedures, the power levers were moved into the beta range. As this occurred when the weight on wheels sensors momentarily recorded an in-air condition, the beta lockout system and engine manual condition activated. This meant that reverse thrust would not be available to assist in decelerating the aircraft during the landing and taxi.
• The increased power setting required to avoid the restricted beta zone while in engine manual mode combined with the long taxi, increased the amount of wheel braking required, resulting in the brakes overheating, failing and igniting.
• The operator did not provide adequate guidance on how to respond to a dual engine control unit or radio altimeter failure on the de Havilland Canada DHC-8-200 aircraft, leaving flight crew without sufficient resources to appropriately deal with such failures.

One Other Factor that Increased Risk was also identified:

• During the evacuation of the aircraft, the BCF fire extinguisher was used on a high temperature brake fire, increasing the risk of exposure to hazardous by-products.

Safety Action taken, in progress, or intended to be taken by Qantas Link in respect of the findings from the event was noted as follows:

• A Technical Advisory Bulletin was issued to DHC-8-200/300 flight crew outlining the event and lessons learned from the event, including relevant technical explanations, such as the radio altimeter failure and the flow-on implications with the beta lockout system.
• The FCOM has been amended to provide additional guidance on the use of brakes.
• An intention to add additional information about the beta lockout system to Section 4 of the FCOM in a future amendment has been notified.
• Work has begun on a revised QRH Checklist for a radio altimeter failure which will assist the identification of a radio altimeter failure and provide appropriate actions and considerations. In particular, it will include text taken from the De Havilland Operating Data Manual which states “If the Radio Altimeter is inoperative or scrolling, ensure positive WOW prior to the selection of Discing on touchdown”.
• Work has begun on a new QRH Checklist for a ‘#1 ENG MANUAL and #2 ENG MANUAL (Caution Lights)’ scenario. This will provide guidance in the event that both engines revert to manual mode, including considerations such as maintaining propeller rpm outside the prohibited range and minimising taxi duration with consideration given to being towed in. It will also state that after landing, both engines should be shut down as soon as practicable and taxi duration must be limited to avoid excessive braking caused by high power settings.

In Conclusion, a Safety Message based on the Investigation Findings was as follows:

This occurrence highlights the importance of appropriate operational guidance, particularly in modern aircraft with complex integrated systems. Procedures for managing an equipment failure should consider factors that may influence the performance of other operational systems. In this occurrence, the flow-on effects of the radio altimeter failure on the beta lockout system. Fortunately, the flight crew were able to successfully troubleshoot the system errors and carry on the flight safely. Increased safety margins in procedural documentation can also help ensure flight crew make appropriate decisions when managing unexpected events. In this case, even a one second change in the timing of retarding the power levers could have prevented the occurrence.

The Final Report was released on 20 February 2024.

Related Articles

• Aircraft Altimeter Failure
• Radio Altimeter
• Airborne Collision Avoidance System (ACAS)
• Terrain Avoidance and Warning System (TAWS)
• Braking Action
• Brakes
• Brake and Undercarriage Fires
• Electronic Engine Control (EEC)
• Weight on Wheels (WoW) Systems
• Quick Reference Handbook (QRH)