Algerie B738 at Lyon on Nov 14th 2019, rejected takeoff due to snow plough on runway/operational error
Last Update: February 15, 2022 / 15:19:05 GMT/Zulu time
The French BEA reported the aerodrome was operating in night conditions, low visibility procedures were active. A ground controller cleared a snow plough onto the runway without coordinating with tower. Both controllers noticed the developing conflict, tower instructed AH-1157 to stop. The crew complied and brought the aircraft to a stop about 1200 meters/4000 feet short of the snow plough. The occurrence was rated a serious incident and is being investigated by the BEA.
On Sep 7th 2021 the BEA released their Final report in French only, an English version is to be expected in due time. The AVH is going to summarize the English version as soon as it becomes available.
On Feb 15th 2022 the BEA released their final report in English concluding the probable causes of the serious incident were:
The runway incursion was linked to an erroneous clearance to enter the runway as a result of a coordination failure between the GND and LOC controllers and keeping the vehicles cleared to enter the runway on the GND frequency.
The following factors contributed to the conflictual clearance and to keeping the use of an inappropriate frequency:
- A high workload in an unusual context where the roles in the tower were sometimes poorly delimited.
- The reopening of the inner runway after snow clearance although the snow clearance of the taxiways to join them to the runway required the snow-clearance vehicles to enter the runway.
- Practices without a clear framework regarding the use of frequencies for the vehicles during temporary runway closures.
- A stop bar configuration incompatible with the snow-clearance paths taken by the vehicles.
The runway incursion, while it can be considered as a failure in itself, is above all else symptomatic of the confusion and disorganization generated by the management of the episode of snow.
The following factors contributed to the confusion and disorganization:
- A Snow Plan whose definition was too formal and in part, disconnected with operational realities.
- Inaccurate measurements of the runway surface condition resulting in a high workload and difficulties with the snow-clearance strategy to be implemented.
- Rules for regulating and suspending operations which were difficult to apply by the persons directly involved in traffic management and snow clearance.
The BEA analysed:
On 14 November 2019, there was a substantial snowfall in the Lyon region. This episode of snow was early in the season. It was forecast and the quantity of snowfall given. However, the relatively high temperatures during the episode of rain in the afternoon led all the actors at Lyon Saint-Exupéry airport to underestimate the coming phenomenon.
The snow clearance operations were activated relatively late; only one of the two runways, runway 35R, had been treated as a preventive measure at around 18:00. The runway snow clearance team composed of a lead vehicle and two snowploughs was operational approximately two hours later.
Runway 35L was closed to clear snow shortly before 20:00. This proved difficult as the runway directly turned white again behind the snowploughs. It was cleared 1 h 45 min later, however the taxiways still had to be cleared of snow and joined to the runway.
When the snowplough lead vehicle asked for clearance to join taxiway A4 with the runway, the GND controller coordinated with the LOC controller. The latter requested that the snowploughs were asked to wait as there was an aeroplane on approach which was going to use the taxiway. A few minutes later, the GND controller was contacted by the lead vehicle again. After the arrival of the anticipated aeroplane, without new coordination, the GND controller cleared the snowploughs to enter the runway and kept them on the frequency.
At the same time, the LOC controller cleared the crew of Air Algérie flight AH1157 to line up and take off.
The GND controller did not follow the progression of the snowploughs and did not detect the conflict. He was discussing the surface conditions with the tower supervisor to help him set up a snow clearance strategy.
The LOC controller’s monitoring of the ground radar screen and the outside environment enabled him to identify the snowplough lead vehicle’s (cleared) entry into the runway safety area. The controller’s request to reject the take-off run and the crew’s immediate reaction meant that a potential ground collision or the possible consequence of a late avoidance manoeuvre were avoided.
GND controller – LOC controller coordination
The SNA-CE OM indicated that the GND controller coordinated any request to enter the runway safety areas with the LOC sector.
An initial coordination took place. However, it was unusual to have to manage snow clearance and the vocabulary used was not standardized. The expression, “do the junctions”, contained an ambiguity as to the need, or not, of entering the runway. The driver of the lead vehicle had removed this ambiguity when making his request to the GND controller, but the ambiguity continued to exist in the coordination between the GND controller and the LOC controller.
After making the vehicles wait and having seen the arrival of the incoming aeroplane, the GND controller, without coordinating with the LOC controller again, cleared the snowploughs to enter the runway. However, six minutes later, the context had changed; there was a new departure and the instructions to wait for the incoming aeroplane before clearing the snowploughs to “do the junctions” were no longer adequate. The GND controller had not kept the departing aeroplane in mind once he had transferred responsibility for it to the LOC controller.
The GND controller did not initiate the exchange with the lead vehicle and probably wanted to reply quickly to the driver without coordinating again. In addition, the GND controller may have been prompted not to coordinate with the LOC controller again in order not to increase the latter’s already high workload.
The effectiveness of the coordination between the GND and LOC controllers thus broke down due to the use of unusual and ambiguous vocabulary. Along with this, the first coordination carried out several minutes previously was not updated.
This coordination was all the more important in that the LOC and GND controllers did not have a shared support showing runway occupancy.
Frequencies used for manoeuvring vehicles
The OM indicated that on accepting a request to enter the runway safety area, the GND controller was to transfer the vehicle to the TWR frequency (managed by the LOC controller). However, the GND controller kept the vehicle on the GND frequency.
This had also been the case when snow was cleared from the previous junction. When the lead vehicle driver asked for clearance to do the first junction between taxiway A3 and the runway, the GND controller cleared the driver after coordinating with the LOC controller assistant. Measurements were being made, vehicles on different frequencies were manoeuvring on the runway while being aware of each other. The fact that the vehicle was kept on the GND frequency was of no consequence at this point.
In practice, it was unusual to keep a vehicle on the frequency despite it entering the safety areas. If a runway was closed with St Andrew’s crosses for example, the LOC sector and GND sector coordinated with each other to manage the crossing of runway 35L, with the approval of the tower supervisor.
On that evening, the St Andrew’s crosses had not been positioned as it was initially thought that the snow clearance operation would not take more than an hour. However, the runway stayed closed for over one and a half hours. During this closure, the vehicles had travelled back and forth between the runway and the parking area, alternating between the TWR frequency and the VEHICLE GND frequency managed by the tower supervisor. Given the duration of the closure, it is possible that the runway was managed in an intermediate way: the logic was neither totally that of a runway closed for a short period with vehicles managed on the LOC frequency, nor totally that specified for the closure of a runway for more than one hour with St Andrew’s crosses.
The GND controller had had the snowplough lead vehicle on his frequency when he held the LOC controller position and when he assisted the tower supervisor (he was then on a break for one and a half hours prior to taking the GND controller position). He had exchanged with the snowplough lead vehicle on the VEHICLE GND frequency when it was manoeuvring on the runway.
The previous exchanges might have resulted in the overlapping of roles in the tower, and the distinction between the frequencies to be used lacking clarity.
The lead vehicle driver was aware that he was not on the correct frequency. The need to change frequency may not have been clarified due to frequencies usually being grouped together at night and due to drivers never taking the initiative to change frequency.
Stop bars and snow clearance circuits
In LVP conditions, the stop bar system protects against runway incursions. The stop bars are lit to avert an unauthorized vehicle entering the runway. Opening the controllable stop bars allows the LOC controller to control entry into the runway safety areas and have an accurate idea of all the vehicles in this area.
The fact that the stop bar lights were reflected in the snow increased the LOC controller's workload. He had to specify to aeroplanes taking taxiway B4 that the red light did not come from the stop bar which concerned them but was the reflection from the stop bar intended to prevent manoeuvres in the opposite direction.
The vehicles’ manoeuvres were limited in the manoeuvring area in LVP conditions. There was a specific route for measurement vehicles designed to minimize the number of times stop bars were crossed. The routes intended for the runway inspection vehicles were not intended for the snow clearance vehicles.
On the day of the incident, when runway 35L was closed, no stop bar was crossed to enter 35L via the access taxiway at the end of the runway. However, when runway 35L was reopened and the stop bars on taxiways A3 and A4 were lit and permanent, manoeuvring on these taxiways to enter runway 35L (and not to vacate it) necessarily meant that they would be crossed making this barrier against runway incursions ineffective.
The BEA also analysed that fairly ineffective de-icing procedures substantially increased the tower's workload for coordination, revising flight plans. As in addition the tower also managed the approach frequencies, the frequency was congested as a result. In addition, the phone lines went busy as well, the BEA wrote:
The tower supervisor was widely called upon to discuss the organization of the snow clearance. There were numerous exchanges with the snowplough lead vehicle concerning the choice of runways or taxiways to be cleared of snow and the condition of the runways. The decisions concerning the regulation of the traffic also led to numerous exchanges, notably with the operational duty manager and the operations manager.
The telephone line and the VEHICLE GND frequency taken together were busy for more than 45% of the time in the hour and a half preceding the event.
The controllers who were no longer on duty had remained behind to provide help in this unusual context. There were seven people in the tower at the time of the event, only four of them had an assigned role.
The LOC controller continued to carry out certain tasks assigned to the tower supervisor which directly impacted the attention he paid to the vehicles and aircraft for which he was responsible.
LFLL 142300Z 23004KT 1800 SN BR BKN002 OVC006 00/00 Q0996 R35R/591591 R35L/591591 TEMPO 0800 SN=
LFLL 142230Z 26003KT 1800 SN BR SCT002 BKN003 OVC008 00/00 Q0996 R35R/591591 R35L/591591 TEMPO 0800 SN=
COR LFLL 142200Z 23003KT 1800 SN BR SCT002 BKN003 OVC008 00/00 Q0997 R35R/591591 R35L/591591 TEMPO 0800 SN=
LFLL 142130Z 00000KT 3000 SN BR BKN002 OVC016 00/00 Q0997 R88/590193 TEMPO 0800 SN=
LFLL 142100Z 29005KT 2000 SN BR BKN002 OVC016 00/00 Q0997 R88/590193 TEMPO 0800 SN=
LFLL 142030Z 26005KT 2000 SN BR BKN002 BKN007 00/00 Q0997 R88/590193 TEMPO 0800 SN=
LFLL 142000Z 27005KT 3200 SN BR OVC002 00/00 Q0997 R88/590193 TEMPO 0800 SN=
COR LFLL 141945Z 28004KT 2600 SN BR OVC002 00/00 Q0997 R88/590193 TEMPO 0800 SN=
LFLL 141930Z VRB02KT 2600 SN BR BKN002 OVC010 00/00 Q0997 R88/590093 TEMPO 0800 SN OVC002=
LFLL 141900Z 30004KT 2900 SN SCT003 SCT010 OVC013 00/00 Q0997 TEMPO 0800 SN BKN004=
LFLL 141830Z 28003KT 2900 SN FEW003 BKN008 OVC012 00/00 Q0997 TEMPO 0800 SN BKN004=
LFLL 141800Z 25001KT 2200 SN FEW007 OVC015 00/00 Q0998 TEMPO 2000 SN BKN004=
This article is published under license from Avherald.com. © of text by Avherald.com.
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