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A320, Macau SAR China, 2018 (1)

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Summary
On 28 August 2018, an Airbus A320 bounced touchdown in apparently benign conditions resulted in nose gear damage and debris ingestion into both engines, in one case sufficient to significantly reduce thrust. The gear could not be raised at go around and height loss with EGPWS and STALL warnings occurred when the malfunctioning engine was briefly set to idle. Recovery was followed by a MAYDAY diversion to Shenzen and an emergency evacuation. The Investigation attributed the initial hard touchdown to un-forecast severe very low level wind shear and most of the damage to the negative pitch attitude during the second post-bounce touchdown.
Event Details
When August 2018
Actual or Potential
Event Type
Human Factors, Loss of Control, Weather
Day/Night Day
Flight Conditions VMC
Flight Details
Aircraft AIRBUS A-320
Operator Beijing Capital Airlines
Domicile China
Type of Flight
Origin Beijing Capital International Airport
Intended Destination Macau International Airport
Actual Destination Shenzhen Bao'an International Airport
Take off Commenced Yes
Flight Airborne Yes
Flight Completed No
Flight Phase Missed Approach
APR
Location - Airport
Airport Macau International Airport
General
Tag(s) Extra flight crew (no training),
Inadequate Airport Procedures,
Destination Diversion
HF
Tag(s) Inappropriate crew response - skills deficiency,
Manual Handling,
Procedural non compliance
LOC
Tag(s) Environmental Factors,
Hard landing
WX
Tag(s) Strong Surface Winds,
Low Level Windshear
EPR
Tag(s) Emergency Evacuation,
MAYDAY declaration
Safety Net Mitigations
Malfunction of Relevant Safety Net Yes
GPWS Effective
Wind Shear Escape Guidance Available but ineffective
Stall Protection Effective
Outcome
Damage or injury Yes
Aircraft damage Major
Non-aircraft damage Yes
Injuries Few occupants
Causal Factor Group(s)
Group(s) Aircraft Operation,
Airport Operation
Safety Recommendation(s)
Group(s) Aircraft Operation,
Airport Management
Investigation Type
Type Independent

Description

On 28 August 2018, the crew of an Airbus A320 (B6952) being operated by Beijing Capital Airlines on a scheduled passenger flight from Beijing Capital to Macau as CBJ7579 mishandled the day VMC landing at destination and the nose gear was destroyed. A MAYDAY was declared and a diversion was made to Shenzhen where an emergency landing was made and an emergency evacuation of all 166 occupants completed. Five passengers needed medical examination and treatment but were not kept in hospital. Inspection of the aircraft found that both engines, especially the left, had sustained significant damage due to ingested nose landing gear debris and there was also deformation damage to both the forward and rear lower fuselage and damage to the runway surface and lighting at Macau and to the runway surface at Shenzen caused by contact with the wheel-less nose gear leg.

Investigation

The Macau Civil Aviation Authority (AACM) assessed the event to be a Serious Incident and therefore carried out an Investigation in conjunction with the Civil Aviation Authority of China (CAAC). Relevant data from the 2 hour CVR and from both the SSFDR and the wireless QAR were available. The CAAC were assisted by Airbus and the French BEA in flight decoding and analysis.

It was noted that the Captain, who had been PF for the flight under investigation, had a total of 9,920 hours total flying experience of which 6,797 hours were on type and 2,808 hours were in command on all types and that the First Officer had a total of 2,591 hours flying experience of which 1,351 hours were on type. A third type-rated pilot was occupying the flight deck supernumerary crew seat as an ‘Observer’ and he had a total of 2,393 hours total flying experience of which 1,610 hours were on type.

What Happened and Why

It was established that the flight had proceeded normally with a stabilised ILS approach using an approach speed (VAPP) of 139 KIAS being flown to 3,360 metre-long runway 34 at Macau until shortly before touchdown. A final wind check given by TWR as the aircraft passed around 1,200 feet was 220° at 7 knots - equivalent to a 4 knot tailwind component and a 6 knot crosswind component. As the aircraft passed 500 feet agl in stabilised flight, FDR data showed that the computed wind velocity was 226° at 26 knots - equivalent to a 10 knot tailwind component and a 23 knot crosswind component. The AP was disconnected at 370 feet with the 10 knot tailwind component computed by the aircraft maintained until below 200 feet agl. However, raw data from the wind sensor located at the runway 34 threshold showed that once the aircraft had descended below 500 feet agl, the detected surface wind had backed to between 170° and 190° and the tailwind component had increased from 10 knots to 22 knots. FDR data showed that as the descent continued from 50 feet agl to 30 feet agl, the airspeed decreased from 133 KIAS to 128 KIAS and the rate of descent increased to almost 800 fpm. Then just before touchdown, a further more sudden (within 1-2 seconds) decrease in airspeed to a recorded 119 KIAS occurred with the aircraft-computed tailwind component recorded as 27 knots at the same time as the crew reported that there had been “a sudden drop onto the runway”. FDR data confirmed that no onboard wind shear warning had been activated.

A hard touchdown (2.36g) followed on the main landing gear approximately 350 metres past the runway threshold and a bounce followed with an initial pitch attitude of around 7½° nose up and the aircraft reached a maximum height of 7 feet agl. FDR data showed that at this touchdown, the thrust levers were not retarded to idle but moved to above the CLIMB detent (between the MCT and TOGA detents), this action being contrary to the applicable SOP which requires the pilot to ensure that the thrust levers are at idle so that ground spoiler deployment occurs since otherwise ‘Phased Lift Dumping’ (PLD), which reduces the severity of a possible bounce at landing by partially extending the ground spoiler under certain conditions, is not activated.

The 7½° pitch attitude led to an automatic callout warning of an excessive nose up attitude in response to which the Captain reduced the pitch attitude to a recorded 1.8° nose down whilst the bounce kept the aircraft in the air. He also reduced the thrust to idle which, because the ‘on-ground’ status is retained for three seconds from last occurrence, resulted in the PLD function activating the ground spoilers. The combined effect of ground spoiler deployment and the negative pitch attitude resulted in a three-point second touchdown four seconds after the first with an even greater (3.41g) vertical acceleration - classified by Airbus as a “severe hard landing”. It was concluded that this impact had caused the disintegration of both nose wheels. Unknown to the crew, the resultant debris was then ingested into both engines.

The landing attempt was immediately rejected and a missed approach procedure was commenced with an observed abnormally low climb rate. Shortly afterwards, TWR advised that fire was observed coming out from its left engine” and a few minutes later, a tyre from the aircraft was found on the runway. On being informed of this, the Captain declared a MAYDAY and began considering which airport would be suitable for a landing, aware that the hard landing had disabled the main navigation system and that the backup navigation system had been activated.

It was decided to divert to Shenzhen, which was approximately 23 nm north northeast of Macau and had more favourable weather conditions, but to first perform a low flypast at Macau to allow ATC there to visually inspect the apparent status of the engines and landing gear. This was inconclusive as regards the nose wheel tyres but was able to confirm the absence of visible fire. En route to Shenzen, the CVR recorded the flight crew briefing the cabin crew on the emergency evacuation to be carried out after landing which specified that it should be conducted through the right side as the left engine may be on fire and also requesting that the emergency services should be in attendance for the landing.

After 43 minutes airborne, the landing at Shenzen was completed with the nose gear being held clear of the runway for as long as possible to minimise further damage to the aircraft and damage to the runway. The pre-planned emergency evacuation was ordered and all 166 occupants exited using the evacuation slides at door 1R and door 4R.

In addition to the destruction of both nose wheels and substantial damage to the leg, a subsequent inspection of the aircraft found extensive damage to both engines, especially to the left, which was all subsequently shown to have been caused by debris ingested from the shattered nose wheels. All 36 left engine fan blades were damaged as were the blades in both the low pressure and high pressure compressors and “melted metal” was found attached to the combustor and both the high pressure and low pressure turbines. This engine also had penetration damage to the fan case and to the leading edge of the inner fan cowl and severe damage to the engine’s acoustic panels. The right engine had also ingested debris but the only significant damage was to six fan blades and two acoustic panels. Considerable damage was also found to the lower forward fuselage which had been significantly deformed following the nose landing gear leg minus wheels making contact with the runway and damage to the lower rear fuselage indicating that a tail strike had occurred during rotation for the go around.

The A320 nose leg minus wheels showing pavement damage at Shenzen (similar damage was also caused to the runway at Macau). [Reproduced from the Official Report]

The Investigation used the recorded flight data to examine the handling of the aircraft following the damage caused by the second touchdown. It was found that the Captain had initiated the go-around “about three seconds” after it had occurred “by advancing the thrust levers to the TOGA position and engaged full nose up input”. The latter action caused the pitch attitude to increase to 15° nose up which triggered a second excess pitch up warning as a tail strike occurred. The Captain responded by reducing the pitch up to around 7.5° and a slow climb out began. FDR data showed that despite the thrust being set to TOGA, although the right engine was at about 90% N1, the left engine N1 was fluctuating between 50 and 60% N1 as a result of ingestion damage. It quickly became apparent to the flight crew that the landing gear could not be raised.

CVR data showed that the TWR advice transmitted around 30 seconds after go-around commencement was somehow misunderstood by the crew since immediately afterwards the right engine thrust lever was moved from TOGA to Idle without any prior communication between the pilots, although upon completion of the movement, one of the pilots could be heard immediately questioning (in Chinese) the equivalent of “is it left or right?” followed by a voice requesting TWR to confirm whether it was the left or right engine which was on fire. There was no response to this except to instruct the flight to “follow standard missed-approach procedure” and although the question was then repeated, there was still no response. It was noted by the Investigation that there had been no engine fire warning and since there was also no evidence that there had been a fire in either engine subsequently found, it was concluded that the ‘fire’ sighted was probably “a spark produced by the high speed abrasion between debris of the fractured nose gear and the rotating parts of the left engine”.

Setting the right engine to Idle with the landing gear still down and the flaps now reset to position 3 in accordance with go-around SOP actions meant that the available thrust was not sufficient to maintain a positive rate of climb and having reached 1047 feet agl, the aircraft then rapidly lost height at up to 1500 fpm as the pitch attitude reached a recorded 14.41° nose up. Initially the mode 3 EGPWS Alert “DON’T SINK” was activated and stall warnings were then annunciated at 950 feet agl for 2 seconds with the AoA at around 15° and again at 765 feet agl for 9 seconds at the same AoA. In response to the second stall warning and after 15 seconds with insufficient thrust had elapsed, the right engine thrust lever was returned to the TOGA position leading to recovery of airspeed and a positive climb. It was noted that the recorded height loss was 425 feet to a minimum of 624 feet agl.[1]

Once this climb had been established, the Captain called TWR again asking for confirmation of which engine had been observed on fire and this time received the immediate response “left engine” and the left engine thrust lever was then “immediately moved to the idle position”. It was observed that the need for the pilots to ask three times and wait 35 seconds to get confirmation of which engine appeared to be on fire had meant that the damaged engine “was left unnecessarily operating at Take-off / Go-around (TO/GA) Mode which could have led to other failures” but also that the initiative taken by the pilots to question and challenge each other’s actions immediately after the right hand engine thrust lever had been moved to the idle position “had contributed positively to the earlier recognition of the error in thrust setting and prevented further altitude loss”.

ATC and Airport Operator Aspects of the Event

It was noted that following the initiation of a go-around from runway 34 by the A320, the runway remained in use and approximately four minutes later, an Airbus A321 being operated by EVA Air on a flight from Taipei to Macau landed on it without subsequently reporting any FOD on the runway. Immediately after this landing, the airport RFFS reported having found a tyre on the runway and TWR then stopped use of the runway for takeoff and landing and requested a runway inspection.

The Investigation noted that the relevant airport operator procedures required that a runway inspection must be carried out “before allowing runway operation when there was confirmed evidence of FOD presence on the runway or aircraft technical problems had occurred with a high possibility of resultant FOD being present”. In association with this requirement, three examples of such “aircraft technical problems” which could have been linked to the investigated event were found as follows:

  • a rejected take-off or landing with hard braking causing tyre burst
  • a landing with gear or brake problems (smoke observed)
  • a landing with fire in the aircraft.

It was noted that the first two of these were “specific technical problems” of which ATC had no information until the tyre was found on the runway. However, it was considered that another “sign of aircraft technical problems” was the abnormal landing with a bounce that was followed by a missed approach with fire then observed coming from the left engine and noted that this had not led to ATC suspending runway operations for an inspection and TWR had instead then issued a landing clearance for the EVA Air A321.

In respect of the finding that, as the aircraft had been about to touch down, there was evidence that low level wind shear of which ATC were unaware had been present, it was noted that the airport had had no equipment to detect the presence of such wind shear and had therefore been unable to alert the flight crew to the risk of encountering it.

Contributory Factors were identified as follows:

  1. For the first touchdown at 2.36g and bounce:
    • Encountered severe low-level wind shear with rapid tailwind increase and downdraft tendency momentarily before touchdown
    • Macau International Airport had no equipment to detect low-level wind shear.
    • The aircraft landed with excessive tailwind.
  2. For the second touchdown at 3.41g with the nose landing gear leading:
    • A normal landing pitch attitude was not maintained after the bounced landing.
    • The thrust levers were moved to idle from above the CLIMB detent during the bounce which resulted in the activation of the ground spoiler by the Phased Lift Dumping function even when the aircraft was actually airborne (due to the system retention of on-ground status for 3 seconds).

Safety Action taken by the Beijing Capital Airlines and known to the Investigation was noted to have included, but not been limited to the following:

  • Implementation of a process to identify pilot skills so as to classify pilots into three categories to be used as a reference for crew pairings, task assignments and targeted trainings.
  • Provision of further online theoretical training on the handling of landing with wind shear, hard landing and a bounce up after a hard landing for all A320 and A330 flight crews.
  • Provision of flight simulator recurrent training on low-altitude wind shear handling, low-altitude go-around and landing deviation control.

Five Safety Recommendations were made as a result of the Investigation as follows:

  • that Macau International Airport evaluate historic runway weather data to determine the case for implementing a low-level wind shear detection system or terminal Doppler weather radar for the detection of hazardous weather conditions. [AR-2018-001]
  • that Macau International Airport review Operational Procedure Document number OP-ATC-07 regarding the “mandatory” runway inspection to be conducted before allowing runway operation when there is confirmed evidence of FOD presence on the runway and aircraft technical problems have occurred with a high possibility that there may be resultant FOD and clearly specify how to determine which aircraft technical problems mean that there is a high possibility that FOD might occur. [AR-2018-002]
  • that Macau International Airport considers implementing an automatic FOD detection system for the timely detection of any FOD present on the runway. [AR-2018-003]
  • that Beijing Capital Airlines incorporates ground and simulator sessions on bounced landing identification and bounce recovery into initial and recurrent training. [AR-2018-004]
  • that Beijing Capital Airlines enhance pilot training to ensure that, in case of a need to perform key changes to critical flight controls/systems based on information provided by external parties, necessary cross-checks are performed with the information available from the aircraft systems and between pilots before such changes are made. [AR-2018-005]

The Final Report was published on 3 April 2019.

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  1. ^ The figures 425 feet and 624 feet are taken from page 20 of the Official Report; contrary figures of 419 feet and 627 feet appear on page 25 of the report.