Description

On 13 January 2016, a Boeing 777-300ER (D2-TEI) being operated by TAAG (Angolan Airlines) on a scheduled international passenger flight from Lisbon to Luanda was fully boarded and ready to depart when an external inspection by the Captain found ice on both the upper and lower wing surfaces which rendered the aircraft unable to depart so the aircraft was towed to a ramp where there was greater exposure to the sun during which manoeuvre the underside of the right side wingtip hit a jet blast deflector. None of the 278 occupants were injured.

Investigation

The event was notified to the Portuguese Accident Investigation Agency (the GPIAA) which carried out an Investigation. It was noted that the aircraft was a Class E type for which ICAO Annex 14 prescribes a minimum of 3.75 metres between an aircraft on any part of a designated stand and any object as long as all obstacles are clear of the engine ingestion danger area. The ramp where the collision occurred was approved for engine ground running or the parking of aircraft up to Class E and was equipped with a perimeter blast deflector.

It was established that the decision to tow the aircraft to the Multi Purpose Ramp (MPR) was taken to minimise the delay to the departure following the Captain’s finding of ice on the upper and lower surfaces of both wings during his pre flight external inspection. It was also a consequence of the fact that the airport had only 8 parking stands which could accommodate class E aircraft and all were either already occupied or were required for inbound aircraft of this class so that the potential difficulty of moving the loaded in-service aircraft to the MPR was accepted - although the risk of doing so was not fully recognised.

The tug performing the task was preceded by an airport operator ‘Follow Me’ vehicle and the allocated aircraft dispatcher and the route followed is indicated below. A wing walker was neither required nor requested. On arrival at the MPR, the aircraft was towed in nose first and then a 180° turn was performed during which the outer part of the right wing was observed to be over, but clear of, the blast deflector at the perimeter of the ramp. It was determined that towing equipment with greater manoeuvrability was required and it was decided to change to a towbarless tractor instead of the one which had initially been used. However, during this changeover, the nose gear was raised and the weight supported by the main landing gear consequentially increased which compressed its shock absorbers and thereby reduced the clearance of the outer wing over the blast deflector and as the manoeuvre re-commenced using the towbarless tractor, the wing came into contact with it and marked the lower wing with a 22 cm scratch and the operation was stopped. To raise the damaged wing clear of the blast deflector, all passengers were disembarked and all cargo offloaded but it was still necessary to also add additional nitrogen to the right main gear shock absorber to move the wing clear. It was considered that “the exchange of towing equipment proved to be not the right decision” since not only was the overhanging wing clearance reduced, the front axis of the towbarless tractor was in very close proximity to the rail on which the jet blast deflector ‘halves’ can be moved and by moving in this direction it passed over them which caused “an oscillation of the aircraft” during which the lower wing surface contacted the blast deflector. It was also observed that the initial offloading of passengers and the holds after the collision was considered to have been inappropriate because the effect was that the wing dropped further onto the blast deflector. The damage caused was minor and was subsequently assessed as being within SRM limits.

The initial mis-positioning of the aircraft on the MPR was found to have occurred in the presence of inadequate instructions given by the Airport Operations Service to the driver of the ‘Follow-Me’ vehicle which led the tug into the MPR. This had resulted in the driver using his discretion to effectively direct the manoeuvre there on arrival. During the 180° turn of the aircraft, the driver had to abandon his vehicle in order to coordinate the operation with no contact with either ATC or Airport Operations in the absence of a portable radio. It was also found that the surface of the MPR was uneven and that this had “contributed to the vertical distance between the lower wing surface and the blast deflector not being uniform”.

Given that Lisbon Airport did not provide aircraft de/anti icing, the Investigation examined the circumstances which led to airframe ice being present at the time of departure. It was found that the aircraft had arrived earlier in the morning from Luanda after a 7 hour overnight flight for a scheduled four hour turnround and a return departure at 1000 hours local time. The TAAG Airlines policy was to tanker fuel into Lisbon to the extent operationally practicable and since a return flight from Luanda to Lisbon typically required around 65,000 kg of fuel against a total tank capacity of 145,500 kg and even if the traffic load northbound was high, most of this fuel could be carried from Luanda without any risk of exceeding the MLW. The effect of this was that after a relatively small fuel uplift in Lisbon - 9,600 kg on this occasion and typically in the range 6000 - 15000 kg - the majority of fuel in the wings was always ‘cold-soaked’ from the northbound flight and received little conductive heating from mixing with the uploaded fuel. At the time of the aircraft’s arrival, it was found that there was 69,100 Litres (55,500 kg) of fuel in the two wing tanks with an approximate temperature of - 16°C and with mist present at the airport and fog in the vicinity, the temperature and dew point were both 7°C. By the time the Captain found frozen deposits on the wings five hours later, the mist and fog had cleared but the temperature had only risen to 10°C just 1° above the dew point. It was concluded that the formation of ice on the aircraft’s wings during the turnround had been a direct consequence of TAAG Airlines’ fuel tankering policy and the relatively low surface temperature, high humidity and the low level of solar radiation.

The formally-documented Findings of the Investigation included the following:

• No pushback briefing was required prior to push back in the SOP in effect at the time of the incident;
• Clear lines of responsibility and delineation of duty were not adequately established in the SOPs between the handling service and the airport operations responsibilities;
• There was no established leadership in the pushback team between the driver and headset man who both work in cooperation with the Airport Ground Operation, without a clearly defined hierarchy;
• The towing manoeuvre involving tight 180° turns of the aircraft was not made according to the FCTM which limits the aircraft weight for this type of manoeuvre to 251,290kg;
• No defined risk assessment had been performed to determine the safety of the intended manoeuvring of the aircraft once it was removed from stand where it had been boarded and loaded, in particular in respect of the clearances from the blast deflector at the MPR;

The combination of Causes which led to the event were determined to have been as follows:

1. The tight tow manoeuvre involving a 180° turn of a class E aircraft within a space surrounded by a 7 metre high obstacle (the jet blast deflector).
2. The pushback procedure which was required in order to position the aircraft so that the obstacle created by the blast deflector was avoided.
3. The non-standard pushback procedure used to position the aircraft at the designated location (the Multi Purpose Ramp).
4. The failure to use a wing walker to manage the wingtip clearance risk.

Four Contributory Factors were also identified:

1. The lack of marks on the ground in the Multipurpose Ramp to facilitate the (intended) towing manoeuvres.
2. The difficulty of moving the jet blast deflector.
3. The absence of any clear pushback team organisation.
4. The risk mitigation for non-standard pushback manoeuvres was not clearly defined.

Nine Safety Recommendations were made as a result of the Investigation as follows:

• that ANA AEROPORTOS DE PORTUGAL should ensure that Lisbon Airport does not authorise manoeuvres involving 180º turns with class E aircraft on the Multi Purpose Ramp – such aircraft should be only parked nose in or nose out taking into account the respective ACN. [14/2016]
• that ANA AEROPORTOS DE PORTUGAL should equip Follow-Me vehicle drivers with a portable radio so that they are permanently in contact with ATC and the Airport Operations Service whenever they are performing aircraft movements in manoeuvring areas. [15/2016]
• that ANA AEROPORTOS DE PORTUGAL should consider the acquisition of a de-icing system appropriate to the operating conditions of Lisbon Airport in order to increase the operational safety of aircraft, avoid towing manoeuvres to other stands or platforms and decrease the risk of operational disruptions. [16/2016]
• that TAAG ANGOLA AIRLINES should not practice fuel tankering (OM-A 8.1.7.5) to destinations without de-icing systems facilities when the forecast weather conditions at the destination are a temperature of 10° C or below and visible moisture is present (clouds or fog with a visibility of one mile or less). [17/2016]
• that ANA AEROPORTOS DE PORTUGAL should ensure that the instructions given by the Airport Operations Service concerning aircraft towing manoeuvres as well as the positioning of the same on the apron or platforms are communicated clearly and unambiguously to Follow-Me vehicle drivers involved. [18/2016]
• that ANA AEROPORTOS DE PORTUGAL, GROUND HANDLING OPERATORS, AIRLINES COMPANIES and the APRON SAFETY COMMITTEE should jointly develop a prescriptive procedure for Non Standard Pushbacks (NSP), which should also address the training and competence of the ground handling personnel responsible for conducting push back manoeuvring. This procedure shall be applied using the pushback simulator as part of the driver approvals procedure. [19/2016]
• that ANA AEROPORTOS DE PORTUGAL and RELEVANT AIRSIDE STAKEHOLDERS AT ALL ANA Airports should review all the procedures implemented internally about airside circulation of vehicles and equipment in the SMS procedures (ICAO Annex 19 ICAO) to ensure the correct Hazard Identification and Risk Assessment process is being applied to all aircraft pushbacks. [20/2016]
• that ANA AEROPORTOS DE PORTUGAL, AIRPORT SAFETY DEPARTMENTS and AIRLINE COMPANIES should update their respective airport Safety Management Systems (SMS) to include pushback risk assessment, ground handling crew coordination and risk mitigation for jet blast in airside operations. [21/2016]
• that LISBON AIRPORT HANDLING OPERATORS (GROUNDFORCE / PORTWAY) and AIRLINE OPERATORS should standardise in their Standard Operating Procedures (SOPs) for the pushback operations to include the following requirements:
  • The composition of a pushback team must be agreed as a Standard Operating Unit (SOU).
  • An SOP must be developed for a pre-pushback briefing which includes a clear delineation of team responsibilities and communication. This shall include designating the team leader for the pushback.
  • A risk assessment of parking stands where non-standard pushback operations are normal procedure should be performed and any requirement for a wing walker identified.
  • Either the wing walker and tug/tractor driver must be in radio communication or the wing walker should be equipped with an aural warning device to alert the tug/tractor driver of any potential conflict.
  • Standard and Non-standard pushback procedures must be developed for all parking stands and included in an SOP. [22/2016]

The Final Report of the Investigation was published on 24 June 2016.

Related Articles

• Risk Assessment
• Hazard Identification
• Aircraft Ground De/Anti-Icing
• Ground Operations
• Ice Formation on Aircraft