Cargolux B744 at Luxembourg on Jan 21st 2010, touched van on runway during landing
Last Update: December 18, 2012 / 00:43:19 GMT/Zulu time
The impaired operational readiness of the ELE department (editorial note: electrical department of the air navigation service provider) due to a manning shortcoming, combined with the lack of provisions to appoint external workforce if necessary, prevented ANA (editorial note: air navigation service provider) to schedule preventive maintenance work outside of normal operating hours (i.e. during the curfew);
- The decision to carry out preventive maintenance work in low visibility conditions without hampering air traffic gave priority to flight operations over safety aspects;
- The lack of adequate co-ordination between aerodrome control tower and ELE department with regard to the preventive maintenance work contributed to a reduced situational and organizational awareness of the TWR control staff;
- Inadequate procedures for the access of vehicles to the RWY and ILS sensitive area during LVP contributed to the development of an unsafe condition;
- Read-back procedures were not adequately applied by aerodrome control tower on ground control frequency, making this procedural safety net ineffective;
- Low visibility weather conditions, associated with the lack of supplementary ground traffic control and surveillance equipment, limited the capability of aerodrome control tower to identify and correct a developing unsafe condition;
- The use of different frequencies for air traffic and ground traffic on the manoeuvring area reduced the situational awareness of ELE 23 maintenance crew working on the RWY, preventing them to take avoiding action.
The AET reported that based on national law and initial assessment the occurrence was originally rated an accident, but following the investigation was rated a serious incident.
Low visibility procedures were in use at the time of the serious incident. Upon contacting Luxembourg approach, while descending through FL154, the crew was told the cloud base was at 100 feet overcast, visibility was 100 meters/330 feet, temperature and dewpoint were at +1 degree Centigrade. The aircraft was vectored for an ILS approach to runway 24, runway visual ranges were reported as 350 meters/250 meters/350 meters.
At that time a maintenance team, callsign ELE 23, was on ground frequency already on the runway after having been cleared directly onto the runway by ground control 22 minutes earlier. The maintenance team parked the van on the runway, had the side doors open while working to be able to hear any radio transmission. The AET reported, there was no other communication on the ground frequency until after the collision over the entire period of more than 22 minutes.
When the Boeing contacted tower, part of the transmission was blocked by another aircraft requesting taxi clearance from the apron to runway 24. Tower cleared that aircraft to taxi from the apron to the CAT III holding point runway 24, then issued landing clearance to the arriving 747, that was about 4.5nm before touchdown at that point. About 2 minutes after receiving landing clearance the aircraft descended through 17 feet AGL, decision height, the pilot flying called "Landing". During the flare the aircraft impacted the roof of the van, which was parked 340 meters past the runway threshold slightly to the right of the runway center line, the roofline at 8 feet above runway surface. The right hand body gear of the 747 hit the van slightly below the roof line and rolled over the entire length of the roof, light bar and antennas were ripped off the vehicle. The two maintenance crew, who had been working on the runway center line lights and had become aware of the arriving aircraft by the noise of the engines, ran off the side of the runway upon the increasing sound. 5 seconds after hitting the van the aircraft touched down on the runway and rolled out without further incident. The pilot flying notice the vehicle and commented during roll out, the pilot monitoring had been watching the instruments and did not notice the van. While vacating the runway the pilot flying radioed tower and reported the vehicle on the runway, the controller asked whether there was any problem which was answered in the negative. The crew taxied the airplane to the parking position.
The AET annotated the crew was not aware of the collision at that time until after arriving at the stand.
After running to the side of the runway and passing of the aircraft the maintenance crew returned to the vehicle and drove it off the runway onto a service road, then attempted to call tower on radio, then, about 3 minutes after landing, called the tower from a mobile phone and reported the collision, the aircraft had ripped the lightbar and antenna of the roof, the pieces of which were on the runway. The crew reported the aircraft had hit the roof with its landing gear and requested the aircraft to be inspected. The tower assistant receiving the call immediately commented that the departure should not be permitted and requested emergency services to perform a runway inspection especially of the first half of runway 24.
The van received substantial damage to its roof structure, superstructure on the roof had been ripped off when the right body gear rolled over the roof.
Tyre #12 on the right body gear sustained multiple cuts and needed to be replaced, the aircraft did not receive any other damage.
The AET reported that the recording equipment of ground frequency was checked for any defects, no anomaly was found within the system. Following the clearance to ELE 23 to enter runway 24 there was no communication on that frequency until after the aircraft had landed.
The AET were not able to establish, whether a runway incursion alert had been triggered or not. The investigation found, that even if a runway incursion alert had been triggered, the aural alert would not be clearly identifyable on the ATC recordings.
The aerodrome data display, which was in evaluation phase and had no operational status, showed the runway had not been blocked at the time of the occurrence, specifically not at the time when the van was cleared onto the runway until emergency services entered the runway to remove the debris from the collision. Two more possibilities existed to mark a runway being in use: a runway incursion alert and a strip marker.
The runway incursion alert would cause the runway display to turn red upon activation of the radio talk button, if the runway had been blocked from that frequency. However, if the runway had been blocked from the other frequency, no alert would occur. Tower and ground were operating on different frequencies.
The report does not mention that a strip marker had been placed to mark the runway blocked.
The ELE department had 7 staff, 2 of them were on sick leave due to an incident that had occurred during maintenance of runway center line lighting earlier. Several incidents regarding runway center line lighting had prompted the air navigation service provider to conduct a meeting with the manufacturer of the runway center lighting which resulted in the decision to conduct preventive maintenance including replacement of the lights. 114 of 161 center line lights had already been replaced when a gas combustion occurred during replacement of another light causing two maintenance workers to receive injuries. This incident prompted ANA to give priority to replacing the remaining 47 lights, however, without hampering air traffic.
The tower controller said in his post incident testimony that he was not aware of the extent of the maintenance work, he had understood in general there had been an accident which required the remaining runway center line lights to be replaced with priority. The tower assistant coordinated with the controller prior to radioing clearance to ELE 23 to enter the runway, the controller however still had no understanding of what ELE 23 was attempting to do and how long they would stay on the runway. The controller remembered that he instructed the assistant to have ELE 23 vacate the runway, when the 747 was about 16-18nm from the runway. He subsequently heard a noise similiar to a portable transceiver and interpreted the sound as confirmation the van had cleared the runway, at the same time there was noise of an incoming telephone call.
The controller further stated that ELE 23 usually consisted of a crew that monitored both ground and tower frequencies. The crew thus would proactivately clear the runway on incoming traffic without tower needing to instruct them vacate the runway. The controller believed the assistant and he therefore believed the noise of the transceiver was the acknowledgement ELE 23 had vacated the runway.
The assistant provided testimony that he had activated the runway incursion function and placed a runway blocked strip marker indicating the presence of the van on the runway. When he saw the 747 inbound to the runway he instructed the van to vacate the runway, heard a radio noise which he interpreted as confirmation the runway was vacated, then was distracted by the incoming phone call. He was astonished that the runway incursion alert activated when he transmitted on the ground frequency for the first time after landing of the 747. The assistant recalled, that during that transmission (recorded by the recording system) he had heard two distinct clicks from the microphone button, one when the button was pushed out of his extended position and another one when the button reached the full down position. It may have been possible that the button was not fully pressed when the instruction to vacate the runway should have been transmitted, the instruction would only be transmitted with the button fully down.
The AET analysed that "it was reasonable to assume that he thought the runway was clear of obstacles and the sensitive area was unobstructed" upon issuing the landing clearance, there was no possibility to visually verify the runway status in the prevailing weather conditions.
There was no communication on ground frequency for 30 minutes after the van was cleared onto the runway.
The AET continued analysis: "Accepting a Â‘carrier waveÂ’ type signal as a confirmation that ELE 23 had vacated the runway and not requiring a proper read-back of the given instruction can be qualified as inappropriate, especially with LVP in force and no visual contact with the van. ... In the present case, not applying standard phraseology to confirm that the runway was effectively vacated rendered that safety barrier ineffective and the lack of additional Â‘engineeredÂ’ defences (e.g. rec. LU-AC-2012/003) or Â‘softÂ’ (e.g. rec. LU-AC-2012/004) defences opened the way to an unsafe condition."
The AET analysed that a Advanced Surface Movement Guidance and Control System Level 2 would have added an active defense alerting the controller of a potentially unsafe condition. Such a system had not been implemented at the time of the occurrence however, though a tender of such implementation had been published.
The AET analysed that even if the crew of the 747 had seen the van at decision height and initiated a go-around, the aircraft would not have avoided ground contact and a collision with the van. The crew could reasonably assume however that the runway was free of obstacles and was focussed to detect visual cues necessary for the landing and did not look out of possible obstacles.
The AET analysed that according to ICAO recommendations all communication associated with the use of a runway should be conducted on the same frequency used for takeoff or landing of aircraft. The use of tower frequency for clearing the van onto the runway would have reduced coordination efforts and the maintenance crew would most likely have heard the communication with the inbound aircraft enabling the maintenance crew to alert tower of their presence and speed the vehicle off the runway.
The AET stated: "Communicating on the same frequency increases the situational awareness for all operators on the same part of the manoeuvring area by providing first hand access to all information transmitted on that frequency."
12 safety recommendations were issued as result of the investigation.
This article is published under license from Avherald.com. © of text by Avherald.com.
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