Description    

On 4 September 2022, a Boeing 777F (D-AALU) being operated by Aerologic on an international scheduled cargo flight from Frankfurt to New York JFK with an augmented crew was taxiing as cleared towards its departure runway in unrestricted night visibility when its jet blast caused several empty airfreight containers to move towards personnel loading another aircraft and one fell to the ground in an attempt to avoid it and sustained a minor injury. 

Two of the containers where they ended up. [Reproduced from the Official Report] 

Investigation

An Investigation was carried by the German Federal Bureau of Aircraft Accident Investigation (BFU). QAR data were available from the aircraft were ATC recorded data including that from ground movement radar. 

The 61 year-old Captain, who was acting as PF, had a total of “about 23,900 hours” flying experience. He was accompanied by a 24 year-old First Officer who had “about 1,390 hours” flying experience and a 39 year old observing Senior First Officer who was occupying a supernumerary crew seat in the flight deck and had “about 2,135 hours” flying experience. The hours on type were not recorded for any of the pilots.  

What Happened

After pushback from stand F235 to face southwest on taxiway N-NORTH (see the illustration below) in accordance with APRON control, the aircraft was cleared to turn left onto taxiway N17, but hold short of taxiway N and call TWR for further clearance. The Captain reported realising that completing this turn would not be possible until beyond the clearance limit given and so came to a stop part way through the turn. TWR then gave further clearance to join and proceed on taxiway N towards departure runway 18. On receiving this, the Captain applied the thrust he considered necessary to begin moving again with the nose gear in a left turn position, leading with the right engine to assist completion of the left turn. He stated that neither he nor the other pilots had perceived any excessive thrust being used. 

Part of the relevant aerodrome diagram showing the stand and taxiway designators. [Reproduced from the Official Report]

Another freighter aircraft was being loaded on stand F234 by three people. According to their statements, two of them were at the rear of the aircraft as the engine thrust of the departing 777 was increased to restart its taxi on receiving clearance from TWR. They saw an empty container move in their direction from a pallet trailer on their stand. As they began to run to get to safety, a second container had passed “very close” to them before coming to rest underneath the right wing of the aircraft they were loading whilst a third was blown from a transfer trolley and ended up beneath the aircraft tail section. They stated that they had not noticed any excessive use of thrust but did see a woman standing next to the wing of the same aircraft who appeared to have been pushed to the ground by the blast. 

Another person who had just overseen the departing aircraft’s push back stated that he had been on his way to the next aircraft when he had felt “quite a strong push in his back” from the jet blast and a container had then overtaken him with a clearance of about 2 metres. He had then turned around and seen two other containers moving, one of which was moving towards the woman who fell as she attempted to avoid it, injuring herself in the process. This person described falling sideways on her hip and shoulder as she tried to avoid one of the containers sustaining injuries to her left shoulder. The container she avoided had come to a stop about 3 metres from her. There was no impact damage to the aircraft being loaded on F234 but the containers which had moved were damaged. 

Why It Happened

Examination of the relevant QAR data showed that after the post-pushback taxi had been completed as far into the turn onto N17 as the initial clearance would allow, the aircraft was on a heading of 210°. To begin the restart, the right engine thrust lever had initially been advanced from to 47% N1 within 7 seconds, whilst the left engine remained at Idle. As the right engine reached 42% N1, the aircraft began to move and the right engine thrust was reduced to 32% N1 over 7 seconds. About 2 seconds after the aircraft had begun to move, the left engine thrust was set to 27% N1 within 4 seconds. Whilst the right engine was running up, its jet blast was directed towards stand F234. The thrust lever angles and achieved N1 in relation to the resulting groundspeed taken from the QAR data show that the right engine thrust increase applied and then reduced only resulted in a 3 knot groundspeed (see the illustration below).

Selected QAR data showing breakaway thrust as the left turn was resumed. [Reproduced from the Official Report]

In general, the aircraft type as loaded (the loadsheet showed a total mass of 282 tonnes) could be expected to produce an efflux wind speed of around 40 knots up to 60 metres from the aircraft if both engines are used similarly but to achieve initial movement when only one engine is used, more thrust is required which produces correspondingly greater efflux wind speeds.

Of note was that not only were the containers which were moved by the jet blast empty, but it was found that although they were initially on pallet cars where hinged safety locks would be used to prevent them moving during transport, these were unlocked.

It was found that relevant general guidance to pilots in the FCTM and FCOM was confined to the need to be aware of what is behind when thrust is above Idle and that although thrust above idle is necessary to begin moving, maintaining movement thereafter will often be possible at idle. However, the AIP entry for the airport was found to state that when taxiing into stands, aircraft “shall generally not stop in curves between the centrelines of apron taxiways or aircraft stand taxi lanes and the centrelines of aircraft stands so as to avoid the further use of break-away thrust”. It also stated that during such manoeuvres, an aircraft which comes to a stop must notify APRON Control and await further instructions before increasing engine thrust again to continue taxiing.

Similar Occurrence 

It was noted that a 2015 jet blast incident at Frankfurt involving a Boeing747-8 which caused damage to two loaded passenger transfer buses and caused minor injuries to one of the passengers had been the subject of a BFU Factual Investigation.

Safety Action was taken as follows:

Aerologic strengthened its procedural instructions for taxi out by stipulating taxiing with synchronous thrust of all engines at all times. 

Airport Operator FRAport advised an intention to strengthen the respective chapter of the AIP with the addition of the following text:

“Aircraft may taxi on the apron only with the absolutely required minimum engine thrust. As a matter of principle, when taxiing (especially in turns) attention should be paid to engine thrust which has to be as synchronous as possible for all operating  engines.”

The Final Report was completed on 22 December 2022 and published the following month. No Safety Recommendations were made.

Related Articles

• Jet Efflux Hazard
• Prop Wash
• Aircraft Load and Trim

Further Reading

• Jet Blast: How Small Changes Can Lead to Big Outcomes, Ulf Henke, Hindsight 34, Winter 2022-23