On 26 June 2017, an Airbus A319 (D-AGWB) being operated by Germanwings on a scheduled passenger flight from Stuttgart to London Heathrow as 4U2464 received and followed a TCAS RA soon after takeoff from runway 07 which resulted from conflicting proximity with an Aerospool WT9 Dynamic (D-AGWB) in day VMC. An EGPWS Mode 3 Alert was generated during the avoidance manoeuvre. Due to the A319 avoidance manoeuvre, the closest proximity was 394 metres laterally and 600 feet vertically.
An Investigation was carried out by the German Federal Bureau of Aircraft Accident Investigation. Data from the A319 QAR was provided by the aircraft operator.
It was noted that the 39 year-old A319 Captain, who was PM for the flight, had an approximate total of 12,244 hours flying experience which included 10,244 hours on A320 series aircraft and that the incident flight was his fourth of the day. The 33 year-old A319 First Officer, a MOL licence holder, had an approximate total of 2,079 hours flying experience of which all but 102 hours were on A320 series aircraft and was on his fifth flight of the day.
The 65 year-old light aircraft pilot “stated that he had a total flying experience of about 382 hours” on powered aircraft which included 83 hours on ultra light aircraft such as the Aerospool WT9. All ATC communications between this pilot and the Stuttgart TWR controller were conducted in German - translations as documented by the Investigation are used in this summary of the event. It was noted that he held an approval which allowed him to enter airport control zones and conduct radio communications in German. The Investigation considered “that he was familiar with radio communication phraseology at airports”.
It was established that the light aircraft pilot, whose aircraft was fitted with an operative transponder, had arrived at the ‘OSCAR’ reporting point at an altitude of 3,300 feet QNH and requested permission to enter the Stuttgart CTR and overfly the airport. In response, the TWR controller had issued a clearance to enter the zone and proceed to a position one mile south of the airport and await a further call for the overflight clearance. On reaching that position, the pilot had reported doing so, adding “I call you back for the overflight”. Half a minute later, the A319 was cleared to line up and wait on runway 07 and one minute after that, the controller advised the light aircraft pilot that an A319 in German Wings colours was at the beginning of runway 07 and that he should report having it in sight which he did. On receipt of this confirmation, he cleared the light aircraft to “cross the airport after the A319 has started”. He then followed this immediately by issuing a takeoff clearance to the A319 and, as it began to roll, asked the light aircraft pilot to confirm that he had the other aircraft in sight which was done. The controller followed this immediately with a reminder that “as I said it might pull up steeply, therefore cross behind it” to which the light aircraft pilot answered “roger wilco”.
However, the light aircraft then left its holding position prematurely and four seconds after the explicit instruction to cross behind it had been acknowledged, the controller transmitted “turn right at once and then overfly, this is not going to work” and received the response “I am turning right“.
Shortly after the A319 got airborne, the controller advised it of the light aircraft traffic at one o‘clock half a mile at 1000 feet and in a right turn, and after a short interval the Captain responded that the traffic was in sight. The controller then followed this with a call to the light aircraft saying “this is not going to work, now fly speedily north” which was immediately acknowledged. Almost straight away, an already active TCAS TA on the A319, which could clearly be attributed to the conflicting light aircraft by reference to the TCAS display, changed to an RA ‘DESCEND’ which required at least a 1500 fpm rate of descent.
The A319 responded as required and began to descend from approximately 1,200 feet agl at 1,600 fpm. It was not immediately possible to report the RA to ATC due to other traffic on the frequency but when it was possible this was done. Soon after the RA descent was commenced, it triggered a Mode 3 EGPWS DON’T SINK’ Alert. The Captain decided that the TCAS RA should be followed, if necessary, up to 400 feet agl and so the EGPWS Alert was ignored. After 10 seconds, the RA was replaced by a ‘Clear of Conflict’ annunciation and the departure climb was resumed. The total descent was approximately 1,500 feet and the ground speeds of the two aircraft during the proximity were approximately 160 knots (A319) and 110 knots (light aircraft).
The A319 Captain subsequently reported that once airborne, they had sight of the light aircraft and had observed it begin to track towards them at an indicated altitude which appeared liable to conflict with their climb. It was apparent from the available QAR data (although not mentioned by the crew) that on receiving the TCAS TA, the A319 climb rate had been reduced so that when the RA began 8 seconds later, the aircraft had almost ceased to climb.
The Conclusions of the Investigation were formally documented as follows:
The airprox of the two aircraft in the departure sector of Stuttgart Airport was caused by the (light aircraft) pilot not following the radio instructions of the tower controller even though he had acknowledged them.
The A319 flight crew deliberately (ignored) the Enhanced Ground Proximity (Alert) during the (TCAS) avoidance manoeuvre.
The Final Report was completed on 6 January 2020 and published the following month. No Safety Recommendations were made and no AIRPROX actual risk category was assigned to the event.