B733, Singapore Changi Singapore, 2020
B733, Singapore Changi Singapore, 2020
On 28 November 2020, a Boeing 737-300F taxiing for an early morning departure at Singapore Changi crossed an illuminated red stop bar in daylight and entered the active runway triggering an alert which enabled the controller to instruct the aircraft to immediately exit the runway and allow another aircraft already on approach to land. The Investigation found that the flight was the final one of a sequence of six carried out largely overnight as an extended duty predicated on an augmented crew. The context for the crew error was identified as a poorly managed operator subject to insufficient regulatory oversight.
On 28 November 2020, a Boeing 737-300F (PK-YGW) being operated by TRI MG Intra Asia Airlines on an international cargo flight from Singapore Changi to Jakarta Halim as TMG019 with an augmented crew was taxiing for departure when it crossed an illuminated red stop bar onto the active runway in normal day visibility. This triggered an alert to the controller who then instructed the aircraft to exit the runway as another aircraft was on approach to land. The subsequent departure was in accordance with further clearances and without further event.
An Investigation was carried out by the Singapore Transport Safety Investigation Bureau (TSIB). Relevant FDR recorded ATC data were available but relevant CVR data had been overwritten.
The Flight Crew
The flight investigated was the last of six consecutive sectors for the flight crew involved. The 37 year-old Captain who was acting as PF for the flight had a total of 5,662 hours flying experience which included 1,576 hours on type and he was operating his third sector of the duty. The 26 year-old First Officer with him had a total of 742 hours flying experience all but 151 hours of which were on type and he was operating his fifth sector of the duty. A second Captain on board as an Augmenting Flight Crew Member and was occupying the flight deck supernumerary seat as required by the applicable regulations when below 10,000 feet. However under those regulations he had no assigned duties and none were assigned by the aircraft operator. Whether this pilot had been wearing a headset for the departure was not recorded. Three other non-pilot employees of the operator were also on board, one on a flight deck seat immediately behind the left side pilot seat and the other two on the rear facing pair of crew seats in the main cabin area located next to Door 1L.
The flight crew’s six-sector overnight duty was scheduled to exceed the maximum permitted two pilot 14 hour flight duty period (FDP) for the starting time involved but with an augmenting crew member, it was noted that this maximum FDP could be increased to 16 hours. The actual FDP worked from the crew’s report time prior to departure from Jakarta Halim the previous evening and their off duty time after arriving back there on completion of the flight from Singapore was 15 hours 35 minutes, just inside the maximum permitted 16 hours for an augmented crew starting a duty at the time they did. It was noted that the aircraft operator’s rostering system did not specify the role to be performed by each pilot during the duty period, rather the crew were left to decide amongst themselves how to share PF/PM/Observer roles.
It was established that the flight had been instructed by the GND controller to via taxiway P, taxiway P1 and taxiway P4 to join the parallel taxiway EP and hold short of its intersection with Taxiway SC1. Whilst following this clearance, the flight was instructed to change the TWR frequency and did so. The TWR controller then cleared the flight to continue on taxiway EP to holding point E11 and hold short of Runway 02 (see the annotated illustration below). The readback of this re-clearance omitted the words “hold short” but the partial readback was not challenged by the controller who considered that as it contained the words “holding point E11” this meant that it had been understood that they did not have clearance to enter Runway 02C and were to hold clear of it on E11. The First Officer stated that he had indeed understood the clearance limit but the Captain stated that “he was informed by the First Officer to continue to taxi via EP and E11 to runway 02C” and that he had not said anything about holding short of Runway 02C or holding at the holding point on taxiway E11 so he had assumed that there was clearance to enter the runway. The Captain also stated that as no traffic was visible on the ND and no other communications had been heard on the TWR frequency, he had “believed that his was the only aircraft using runway 02C”
An overview of the taxi route along the parallel taxiway to the runway 02C holding point. [Reproduced from the Official Report]
As the flight approached taxiway E11, the Captain asked the First Officer to run the Before Takeoff Checklist and as this was being done, the flight continued from taxiway E11 onto runway 02C without stopping. According to the First Officer’s account, as this happened he had been busy reading out the requested Checklist and noting the Captain’s responses and “did not have a chance” to remind him that they did not have clearance to enter the runway. In his account, the Captain stated that he “did not notice the red stop bar lights in front of the runway holding position marking nor the runway guard lights”. The second Captain occupying the centrally positioned supernumerary crew seat stated that he “had not been paying attention to” the First Officer’s exchanges with ATC and was unaware that clearance to enter the runway had not been given.
Immediately after the aircraft passed the holding point/clearance limit on taxiway E11, the installed Microwave Barrier Detectors (MBDs) located just after the holding point activated an alert to the controller. At this time, another aircraft was on an approximate 3nm final approach to land on runway 02C and so the controller immediately instructed the 737 to vacate the runway onto taxiway E10. This instruction was acknowledged and actioned which enabled the controller to then issue a landing clearance to the approaching aircraft. Once it had landed, the 737 was cleared for takeoff and the rest of its flight was uneventful.
According to the flight crew “they would typically cross-check with each other on whether take-off/line-up clearance had been obtained before lining up on the runway for departure (as) this was part of their training and was stipulated in the aircraft manufacturer’s (FCTM)”. However, such a cross-check was not included in the operator’s Before Takeoff Checklist and instead, it was specified that the PM was responsible for remembering to carry out such memory items. It was found that the Boeing Before Takeoff Checklist as used by the aircraft operator contained only two items - ‘Flaps’ and ‘Stabiliser trim’. According to Boeing, this Checklist includes “only the minimum items needed to operate the aircraft safely (so) the cross-checking of clearances, which is considered basic airmanship, is not included". Boeing leaves it up to individual aircraft operators to decide if they wish to add other items to these ‘essential item’ checklists. Boeing also states that the Before Takeoff Checklist “is meant to be completed before entering the runway to avoid high workload period such as taking off from a runway”.
Other relevant information included:
- Between the time when the aircraft checked in on the TWR frequency and the incursion, there were no communications with any other aircraft on that frequency.
- Enhanced centre taxiway centreline marking is provided immediately prior to the runway holding point as an additional alert to pilots that they should be prepared to stop unless clearance to enter the runway has been received.
- MBDs are linked to the corresponding holding point stop so that they are only active when the stop bar is red.
- It was confirmed that at the time of the incursion, all relevant airport and ATC equipment had been operating normally.
- The pilots involved confirmed that they had been adequately rested prior to commencing their FDP.
- In respect of the absence of any assigned duties to a third pilot required to occupy the flight deck supernumerary crew seat, the aircraft operator stated that it expected any pilot in such a role “to pay attention to the operation of the flight (including radio transmissions) and monitor the actions of both the PF and PM during take-off and landing” although this expectation was not documented and no evidence was found that pilots are made aware of this expectation.
- Although an aircraft commander may assign duties to a pilot fulfilling a required supernumerary role, no such duties were specified by the Captain in command for the incursion sector nor had he assigned any such duties to himself when fulfilling that role during previous sectors.
- The operator did not set any limit on the maximum number of sectors which could be flown within the maximum duty time and no such requirements were included in the applicable regulatory requirements for short haul flights. However, it was noted that the ICAO Doc 9966 ‘Manual for the Oversight of Fatigue Risk Management Approaches’ does suggest this.
- No guidance was provided by the aircraft operator in respect of how pilots who were part of an augmented crew required for FDP compliance purposes should rest during flight when not required to be on the flight deck, although the applicable regulatory requirements did specify that “a passenger seat” must be available for that purpose. Those regulatory requirements were found not to define “a passenger seat” but the Investigation team “understood from the State of the Operator that none of the seats in the aircraft involved met the requirements of a passenger seat”.
- The aircraft operator issued sleeping bags to all three pilots and advised that an augmenting flight crew member could, when not required to be on the flight deck, “choose to rest in a sleeping bag on the galley floor” although it was noted that there was no restraint system for any person resting in such a sleeping bag.
- No evidence was found that the aircraft operator had regulatory approval to substitute the required passenger seat with a sleeping bag.
- The First Officer acting as PM at the time of the incursion had only been able to rest for under two hours during the previous five sectors, in four of which he had also been a member of the operating crew throughout.
The Cause of the investigated Runway Incursion was determined to have been “the PF assuming that ATC clearance had been given for their flight to enter the runway and their failure to notice that the red stop bar lights were illuminated, indicating that the flight was to stop at the holding point on taxiway E11”.
Other Findings in relation to the event were, in summary, as follows:
- It was suspected that both pilots may have been suffering from some degree of tiredness, considering that they had been on duty for more than 13 hours at the time of the event.
- The aircraft operator’s flight rostering system did not allocate the roles of the three pilots involved and they were free to decide amongst themselves how to share these duties during their six sector FDP. This resulted in an arrangement whereby the two Captains each operated three sectors in command and rested on the rest apart from one of them doing a fourth sector as a First Officer to reduce the First Officer’s operating sectors to 5.
- The aircraft operator did not include cross-checking of line-up/take-off clearance in the Before Takeoff Checklist since such cross-checking was treated as a memory item. In the investigated event, there was no cross-checking of the line-up clearance.
- There were a number of instances in the lead up to this incursion where the flight crew’s performance in terms of CRM was not optimal.
- The Relief Captain was available as a crew resource on the flight deck but was not assigned any duties.
- The State of the Operator’s regulations require the availability of a passenger seat as a condition for the extension of maximum duty time by using an Augmenting Flight Crew Member (in this case the Relief Captain) to operate a flight or flight sequence but there was no passenger seat in the aircraft.
- The aircraft operator issued sleeping bags to the flight crew so that they could rest in them on the galley floor when they were not required to be on the flight deck. However, there was no restraint system for the person resting in such a sleeping bag and there was no evidence that this resting arrangement was acceptable to the State of the Operator.
- In determining the maximum duty time, the aircraft operator did not include the number of sectors as a planning parameter. Also, the State of the Operator did not have a requirement for the aircraft operator to include the number of sectors for short haul flights as a planning parameter when determining duty time limits.
Safety Action taken during and known to the Investigation as a result of the event was noted to have included the airport ANSP conducting a Safety Briefing for all its controllers in August 2021, with discussions focusing on how ATC can provide information to improve pilots’ awareness of traffic. This Safety Briefing also provided information on how human performance might be affected by very low traffic volume situations as a result of COVID-19 which both pilots and air traffic controllers are unaccustomed to.
A total of eight Safety Recommendations were made as a result of the Investigation as follows:
- that the State of the Operator (Indonesia) consider requiring its aircraft operators to include the number of sectors as a planning parameter when determining the maximum duty time for short haul flights. [RA-2021-003]
- that the State of the Operator (Indonesia) review the appropriateness of the aircraft operator’s practice of allowing its flight crew to rest in a sleeping bag on the galley floor. [RA-2021-004]
- that Tri MG Intra Asia Airlines remind its flight crew to be alert when approaching the active runway and to never cross illuminated red stop bar lights without authorisation from the Air Traffic Control. [RA-2021-005]
- that Tri MG Intra Asia Airlines assess the need to include an item on line-up/take-off clearance before entering a runway in its Before Takeoff Checklist. [RA-2021-006]
- that Tri MG Intra Asia Airlines consider including the number of sectors as a planning parameter when determining the maximum duty time. [RA-2021- 007]
- that Tri MG Intra Asia Airlines review its practice of allowing its flight crew to rest in a sleeping bag on the galley floor. [RA-2021-008]
- that Tri MG Intra Asia Airlines consider assigning duties to an augmented flight crew member to better utilise crew resources. [RA-2021-009]
- that Tri MG Intra Asia Airlines review its flight crew rostering system with a view to ensuring a more even distribution of flight duties and rest periods. [RA2021-010]
The Final Report was published on 26 August 2021.
- Runway Incursion
- Augmented Flight Crew
- Read-back or Hear-back
- Runway Incursion Prevention - Runway-holding Position, Stop Bars and ATC Clearance
- Safety Oversight