On 29 May 2009, a Boeing 757-200 being operated by UK Airline Thomson Airways on a passenger charter flight from Sharm-el-Sheikh, Egypt to Dublin and having just landed on runway 10 at destination at night in poor visibility overtook a small ride-on grass mower moving along the right hand side of the runway in approximate line with the aircraft’s right hand wing tip. The driver of the mower was unaware of the arriving aircraft until he heard it on the runway behind him. Prior to the landing, ATC had been informed that all grass-cutting equipment previously working on and around the runway had cleared it.
An Investigation into this event was carried out by the Irish AAIU.
It was established that with the Boeing 757 already cleared to land and on approximately 2 mile finals one minute prior to touchdown, the ASMGCS recording showed the targets representing the aircraft and the ride-on mower on the landing runway both becoming highlighted in red, indicating the development of a potential conflict situation. Having previously asked the grass cutting team to clear the runway and cease operations altogether because of the deteriorating visibility, the AMC asked the supervisor about the disposition of the three vehicles involved in grass cutting and was told that they were clear. There were no further communications prior to the aircraft landing and the ASMGCS recording shows that soon after touchdown, the aircraft passed the ride-on mower whilst at an estimated ground speed of 96 kts. The mower was moving in the same direction as the aircraft approximately 18.5 m to the right of the runway centreline. The wingspan of a Boeing 757-200 is 38.05 m.
The Investigation found that as visibility deteriorated LVPs had been initiated and all the necessary checks completed more than one hour before the conflict occurred, but that they were not enforced until after the landing despite the fact that they were required at least 25 minutes prior to the conflict because of a lowering cloud base. Since a requirement of LVPs is that the manoeuvring area is clear of all obstructions such as machinery, plant, maintenance vehicles, contractors, earlier implementation of LVPs would have meant a cessation of grass-cutting.
Following is an image taken from the AAIU Report showing ASMGCS screen at the moment that the aircraft passed by the ride-on mower. The image is oriented with south at the top and thus the direction of travel of the aircraft and the mower on the easterly runway is from right to left. The aircraft can be seen on the centreline with the port wing clearly defined. The other wing is ill-defined because of shielding by the radar antenna.
Schematic of lawnmower next to runway
After the interim issue by the AAIU of a Preliminary Report on 30 June 2009 which contained an Interim Safety Recommendation to the Dublin Airport Authority that it “should ensure that all vehicles, which are required to operate on or in close proximity to active runways should be equipped with airband VHF radios capable of being selected to ground control and tower frequencies, and also with flashing yellow light beacons and transponders compatible with the ASMGCS system”, a response was received that this had already been done.. A range of other actions were also taken by the Airport Authority during the course of the Investigation to address procedural, equipment and personnel training deficiencies relating to grass cutting.
The Investigation also found that the SMR system that was available to ATC had not detected the ride-on mower on the runway due to its limited ground surveillance capability. The Probable Cause was identified as “The failure of the driver of the ride-on mower to vacate the runway after he had been instructed to do so.”
The Final Report may be seen in full at SKYbrary bookshelf: AAIU Report No: 2010-002, Published: 03/03/10
It included one further Safety Recommendation to the Dublin Airport Authority that they should “review their training programmes, including the frequency of refresher training, for all operatives who are required to drive on the manoeuvring area. Reference to ICAO Doc 9870 AN/463 “Manual on the Prevention of Runway Incursions” should be included in all such training programmes. (SR 02 of 2010)