Singapore A333 at Yangon on Nov 25th 2019, tail strike on landing

Last Update: June 30, 2021 / 08:18:37 GMT/Zulu time

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Incident Facts

Date of incident
Nov 25, 2019

Classification
Accident

Flight number
SQ-998

Destination
Yangon, Myanmar

Aircraft Registration
9V-SSI

Aircraft Type
Airbus A330-300

ICAO Type Designator
A333

Airport ICAO Code
VYYY

A Singapore Airlines Airbus A330-300, registration 9V-SSI performing flight SQ-998 from Singapore (Singapore) to Yangon (Myanmar) with 282 passengers and 13 crew, landed on Yangon's runway 21 at 09:07K (02:37Z), however, the tail contacted the runway surface on landing. The aircraft rolled out without further incident.

The aircraft was unable to continue the schedule and is still on the ground in Yangon about 11 days after landing.

A replacement Boeing 777-200 registration 9V-SVB positioned from Singapore to Yangon, performed the return flight SQ-997 and reached Singapore with a delay of 7.5 hours.

On Dec 6th 2019 Myanmar's AAIB reported the tail of 9V-SSI scratched the runway surface of Yangon International Airport on arrival from Singapore. Myanmar's AAIB is investigating the occurrence.

On Nov 23rd 2020 Myanmar's AAIB released a notification stating there were no injuries, the aircraft sustained substantial damage when the aircraft suffered a tail strike on landing at Yangon. The final report is already being drafted.

Myanmar's AAIB released their final report concluding the probable cause of the accident was:

During the landing, the pitch up inputs by the PF caused the aircraft to reach a maximum pitch angle of 10.7 degrees, resulting in the tail strike.

In the findings the AAIB stated:

- During the event landing, the PIC repeatedly gave instructions to the PF to “hold the attitude” with the intention for the pitch attitude to be maintained.

- The PF’s understanding of the phrase “hold the attitude” was that the aircraft was losing its pitch attitude, hence he provided pitch up input to his sidestick.

- The PIC, who was the PM, did not announce “PITCH PITCH” in the three instances when the pitch angle of the aircraft exceeded 7.5 degrees, as required by the operator’s procedures.

- The PIC, who was acting in the capacity of an instructor pilot, did not take over controls or provided dual input to control the aircraft despite repeating his instructions “hold the attitude” four times over 12 seconds.

The AAIB reported the crew consisted of a captain under training (44, ATPL, 13,926 hours total, 2.5 hours on type) in the left hand seat being pilot flying, the pilot in command and instructor (52, ATPL, 19,080 hours total, 688 hours on type) in the right hand seat and a safety pilot (50, ATPL, 9,522 hours total, 1,213 hours on type) seated in the observer's seat.

The AAIB summarized the sequence of events:

At the top of descent, the PF informed the PIC that he would initiate flare earlier at 50ft above ground level (AGL) to compensate for the upslope of the runway and the expected tailwind.

At 09:06:15, when the aircraft was at 2150ft AGL, the autopilot was disengaged and the PF performed the manual approach to land the aircraft on Runway 21. At 09:08:30, the PF initiated flare when the aircraft was passing 100ft AGL. One second later, the PIC said “flare” twice to which the PF responded by providing more pitch up input.

The exchange between the PIC, PF and SP over the next twelve seconds was as follows:

09:08:34 PIC: Alright and good
09:08:36 PIC: Okay never mind and just hold the attitude
09:08:39 PIC: Spoilers
09:08:40 PIC: Oh hold the attitude
09:38:41 SP: Nose attitude
09:38:41 PIC: Hold
09:38:41 SP: Nose attitude too high
09:38:41 PIC: Hold the attitude
09:38:43 PIC: Hold the attitude
09:38:44 PF: Okay

At 09:08:34, during the above exchange, the first Weight-on-Wheels (WOW) Ground signal was recorded for both the left and right main gears, indicating the first instance where landing gear made contact with the surface of the runway. At this first instance of touchdown, the aircraft heading was 212.9 degrees, the indicated air speed (IAS) was 136 knots and the pitch angle was 7.21 degrees (nose up).

The recorded WOW signal for both the left and right main gear indicated a bounced landing as the following was observed over the next three seconds:

09:08:35 – left and right main gear WOW signal changed from Ground to Air
09:08:37 – left and right main gear WOW signal changed from Air to Ground

Throughout this period – nose gear WOW signal remained as Air

Two seconds after the main gears touched down for the second time, both thrust reversers were deployed and a further second later, the ground spoilers were extended. During this period, the pitch command from left side stick changed from -6.58 to -16.44 degrees, indicating that the PF intended for the aircraft to pitch up further. The pitch angle of the aircraft was at 8.61 degrees (nose up) just as the thrust reversers were being deployed, decreasing to a minimum of 5.10 degrees two seconds later before increasing to a maximum of 10.72 degrees a further two seconds later, when both the thrust reversers and ground spoilers were fully deployed.

The thrust reversers for both engines were stowed at 09:08:52 and the nose gear made contact with the runway at 09:08:54. The aircraft turned off the runway at 09:09:33 and taxied to its parking bay. According to the flight crew, they were unaware that a tail strike had occurred and were only made aware when a ground maintenance personnel informed them that damage to the tail section was observed during the post flight check.

The aircraft sustained substantial damage, in particular:

- Fuselage Lower Skin between frames 68 and 73 in the tail section were dented, scratched and torn
- Fuselage frames between frames 60 and 73 in the tail section were bent and scratched

The AAIB analysed:

Communications among the flight crew

During the sequence shortly after the aircraft landing gear contacted the runway, the PIC said, “Hold the attitude”. At one point, the SP mentioned “nose attitude too high” to which the PIC replied “hold the attitude” twice.

In the post incident interviews, the PIC indicated in those instances that he mentioned “hold the attitude”, he intended for the PF to maintain the aircraft’s pitch attitude at its current position. On the other hand, the PF indicated that when he heard the PIC saying, “hold the attitude”, his understanding was that the aircraft was losing its pitch attitude. This was consistent with his reaction where he pulled back on the sidestick to provide pitch up inputs shortly after each instance of the PIC saying, “hold the attitude”.

The difference in understanding of the phrase “hold the attitude” appears to have contributed to the PF providing additional pitch up inputs. The net effect of the PF’s cumulative pitch up inputs led to the aircraft’s pitch attitude reaching a maximum value of 10.7 degrees which was the likely instance where the tail strike occurred.

The duty of the pilot monitoring (PM)

According to the operator’s procedures, the PM should monitor the pitch angle and announce “PITCH PITCH” when it exceeds 7.5 degrees nose up attitude. The aircraft was porpoising during the initial touchdown and the pitch angle of the aircraft exceeded 7.5 degrees three times during the 12 seconds period prior to the tail strike.

The PM recalled that during that period, he was paying attention to the external environment to ensure that the PF controlled the aircraft to maintain it along the runway centerline. The absence of “PITCH PITCH” in the CVR audio track suggests that the PM did not notice the PFD showing that the aircraft pitch angle had exceeded 7.5 degrees.

Pilots should be mindful that when an aircraft is not installed with the predictive tail strike prevention system, the PM’s role in monitoring the aircraft’s pitch angle is even more critical in detecting an impending tail strike and alerting the PF to react to the situation.

Taking over of controls

The PIC, acting as the role of the PM, did not consider taking over the controls or providing control inputs through his sidestick during the event. According to the PIC’s assessment at that point, the PF was able to respond to his instructions and reacted appropriately, and the safety of the aircraft was not gravely compromised. Therefore, the PIC did not intervene.

It is challenging for instructor pilots to determine the appropriate time to take over or intervene with the control of the aircraft. Intervening too early will deprive the trainee of his learning opportunity while too late, the safety of the flight might be jeopardized.

To the extent that the PIC repeated the “hold the attitude” instruction four times within 12 seconds, it indicates that the PIC was concerned with the attitude of the aircraft during the landing. The landing and take-off, phases are statistically the more dangerous phases of flight. As such, instead of providing repeated instructions to the PF, it might have been more prudent for the PIC to be more decisive in providing dual inputs through his sidestick to correct the attitude of the aircraft.

Metars:
VYYY 250400Z 33004KT 8000 NSC 30/21 Q1015 NOSIG=
VYYY 250330Z 06004KT 7000 NSC 29/22 Q1015 NOSIG=
VYYY 250300Z 01004KT 7000 NSC 28/24 Q1015 NOSIG=
VYYY 250230Z 02005KT 6000 NSC 26/25 Q1015 NOSIG=
VYYY 250200Z 01005KT 6000 FEW020 26/25 Q1015 NOSIG=
VYYY 250130Z 34004KT 6000 FEW020 25/23 Q1014 NOSIG=
VYYY 250100Z 35004KT 6000 NSC 24/23 Q1014 NOSIG=
VYYY 250030Z 35004KT 6000 NSC 24/23 Q1013 NOSIG=
VYYY 250000Z 34004KT 6000 NSC 24/23 Q1012 NOSIG=
VYYY 242330Z 01003KT 6000 NSC 24/23 Q1012 NOSIG=
VYYY 242130Z 35002KT 6000 NSC 24/23 Q1011 NOSIG=
Incident Facts

Date of incident
Nov 25, 2019

Classification
Accident

Flight number
SQ-998

Destination
Yangon, Myanmar

Aircraft Registration
9V-SSI

Aircraft Type
Airbus A330-300

ICAO Type Designator
A333

Airport ICAO Code
VYYY

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