On 11 May 2018, a Bombardier CRJ1000 (PK-GRJ) being operated by Garuda Indonesia on a scheduled domestic passenger flight from Tambolaka to Kupang as GIA460 and an ATR72-500 (PK-WFW) being operated by Wings Air on a scheduled domestic passenger flight from El Tari to Tambolaka as WON1921 lost safe separation in day VMC within Class ‘G’ airspace in which only Flight Information Service was provided. A coordinated TCAS RA resulted and was followed by both aircraft and the conflict was thereby avoided. The minimum vertical separation was 428 feet when 1.3 nm apart laterally.
An Investigation was carried out by the Indonesian National Transportation Safety Committee (NTSC) - the Komite Nasional Keselamatan Transportasi (KNKT). Relevant CVR data were overwritten but both aircraft operators provided QAR data covering the event and a full recording of air traffic communications between the two aircraft and the Tambolaka Aeronautical Communications Officer (ACO) was available.
It was noted that the 31 year-old CRJ1000 Captain, who was PF for the flight had a total of 5,776 flying hours experience but the amount of this time on type was not given. Their 27 year-old First Officer had a total of 795 flying hours experience but the amount of this time on type was also not given. The flying experience of the ATR72 pilots was not given. Flight Information Service at Tambolaka was provided by a 29 year-old “Aeronautical Communication Officer”. All those involved were Indonesian nationals with valid qualifications for their jobs. The Investigation noted that the day before the occurrence, the CRJ1000 Captain had felt unfit during his morning flight duty but after finishing his duty at midday had rested at his hotel and the following day had “felt better”. However, the following day he was hospitalised and diagnosed as having typhoid.
It was established that when the Wings Air inbound flight was about 56 nm from Tambolaka at 14,500 feet, the crew had advised the ACO that they were about 15 minutes away and this was acknowledged. Meanwhile, the Captain of the about to depart Garuda flight had briefed his First Officer that after takeoff, they would climb to about 400 feet aal before turning left to join airway W43 and continuing the climb. He subsequently stated that this was the usual Garuda Indonesia departure procedure for Tambolaka although the Investigation concluded that, in the absence of any evidence that this was a documented company procedure, it was in fact merely ‘custom and practice’.
One minute after the departing aircraft had requested and received engine start approval from the ACO, the inbound aircraft announced that it was now 36 nm from Tambolaka and requested descent and was instructed to descend to 10,000 feet and call reaching. A couple of minutes later, the departing aircraft called ready to taxi and was instructed to taxi to runway 10 and report ready for departure. The ACO then called the inbound aircraft to request its position and was told it was “about 23 nm on radial 096° from Tambolaka passing 11,500 feet” and the ACO then informed it that a CRJ1000 aircraft with the callsign GIA460 was entering runway 10 to backtrack. On being then told that the inbound aircraft had reached 10,000 feet, the ACO instructed it to descend to circuit altitude and join left downwind for runway 10 which was correctly read back. As the CRJ1000 was backtracking, its Captain “advised the PM that the inbound flight would be joining downwind right hand for runway 10".
When the CRJ1000 PM advised that they were ready to receive their departure air traffic control clearance, the ACO responded by first getting another position report from the inbound aircraft and was told they were 14 nm out and crossing the 096° radial from Tambolaka passing 8,000 feet and confirmed that they would join downwind left for runway 10. The ACO then transmitted “Garuda 460, cleared to Kupang level 250 squawk 5615, runway is clear” and after readback and confirmation that the departing aircraft was aware of the inbound traffic, the CRJ1000 called that it was “rolling for takeoff”. The inbound aircraft responded that it had noted this and was joining downwind left for runway 10 with “the runway in sight via coastline” and the CRJ1000 responded with a request that they call downwind. Shortly after this, the CRJ1000 reached about 600 feet on the extended runway centreline and began a left turn.
One minute after this turn had been commenced the ATR72 received a TCAS RA ‘DON’T DESCEND’ against the CRJ1000 when the two aircraft were 1.8nm laterally and 660 feet vertically apart. The inbound ATR72 was making a gentle right turn and passing a heading of approximately 290° and the outbound CRJ1000 was making a gentle left turn and passing a heading of approximately 020°. Two seconds later, as the ATR72 began to level off, its RA changed to ‘CLIMB’ and the CRJ1000 AP was disconnected and one second after this, the CRJ1000 received a ‘DESCEND’ RA. The minimum vertical separation of 428 feet was reached three seconds later (in the positions marked on the illustration below as 1452:55) when the two aircraft were 1.3 nm apart and the CRJ1000 was just beginning its TCAS descent. Three seconds later, the ATR72 RA ceased after lasting 9 seconds but the CRJ1000 RA continued for a further 40 seconds until it had descended 400 feet. FDR position coordinates from the two aircraft were used to calculate the separation between the two aircraft as the conflict developed and was resolved. The following illustration superimposes the FDR data on a Google Earth map.
The annotated ground tracks of the two flights. [Reproduced from the Official Report]
The Investigation noted that:
- The CRJ1000 First Officer either failed to recognise that the Captain’s statements about the inbound aircraft joining downwind right hand were contrary to the ATR72 crew’s three broadcasts of their intention to join downwind left hand, the third of which he had specifically and correctly acknowledged, or for some reason consciously did not correct him.
- the CRJ1000 pilots’ Navigation Displays (ND) on which traffic visible to TCAS is displayed would have shown the relative position and altitude of the inbound ATR72 to the left / north side of the CRJ1000 initial climb after takeoff were such that the subsequent left turn and climb would have clearly taken the aircraft into potential conflict with it.
- in continuing to perform the flying duty during which the event occurred, it was clear that the CRJ1000 Captain “did not consider that his medical condition might degrade his performance”.
- It was considered that since the initial call to the departing aircraft by the Tambolaka ACO was not prefaced by the unit’s full callsign - Tambolaka Aerodrome Information – this might have led the Captain to confuse the type of service being provided as air traffic control rather than flight information.
- Some of the information passed by the ACO to the CRJ1000 used instruction phraseology and the crew sometimes requested a clearance from the ACO. It was considered that “these mixed-up communications” indicated a lack of clarity as to whether the service status was that of air traffic control or flight information which might also have led the crew to assume that the flights would be separated by the ATS provider.
- The manner in which the departure clearance was relayed to the departing CRJ1000 by the ACO as a clearance to fly at altitude 25,000 feet to Kupang did not contain the clarification that this clearance applied only upon entering Kupang airspace which it was considered might have led the Captain to incorrectly assume that the flight was approved to continue climb to altitude 25,000 feet without restriction - it was noted that the pre-selected target altitude had been set to this figure prior to takeoff.
The Investigation formally identified the Contributory Factor in respect of the occurrence as “pilot justification based on available information of the inbound ATR72 that was not properly assessed and without proper crew coordination this resulted in the CRJ1000 departing following the common practice to turn left after departure”.
Five Safety Recommendations were made as a result of the Investigation as follows:
- that AirNav Indonesia should ensure that all phraseology used while providing flight information services are conducted in accordance with the ATS SOP to make clear determination of service status air traffic control services and flight information services. [04. A-2018-18.01]
- that Garuda Indonesia emphasise the (use of the) reporting system including self-assessment reports to ensure that medical conditions which may degrade pilot performance can be identified and mitigated in a timely manner. [04. O-2018-18.02]
- that Garuda Indonesia ensure that all pilots implement Crew Resource Management described in the OM-Part A. [04. O-2018-18.03]
- that Garuda Indonesia ensure that all pilots are aware that air traffic control service that includes traffic separation is not provided in Class ‘G’ airspace (and that) the separation between aircraft is the responsibility of each pilot based on their decision. [04. O-2018-18.04]
- that Wings Air ensure that all pilots are aware that air traffic control service that includes traffic separation is not provided in Class ‘G’ airspace (and that) the separation between aircraft is the responsibility of each pilot based on their decision. [04. O-2018-18.05]
The Final Report of the Investigation was released on 23 July 2020.