UK investigators have warned that the intensity of single-runway operations at London Gatwick, arising from pressure to meet capacity targets, threatens the hub's ability to conduct runway inspections safely and effectively.

This conclusion by the Air Accidents Investigation Branch follows a probe into an inspection vehicle's being cleared to enter runway 26L while an arriving Aer Lingus Airbus A320 was still rolling on the runway 12s after touchdown.

It had landed in light rain and a 3kt tailwind and was heading towards the intended rapid exit designated FR, at around 60kt, when the vehicle entered the runway, turning towards the A320.

"The [captain] had been surprised to see the vehicle entering the runway and believed the vehicle’s clearance had been conditional on the aircraft vacating first," says the inquiry into the incident on 3 February last year.

As a result of the captain's filing a safety report the air traffic control provider for Gatwick carried out its own investigation.

This investigation suggested there was nothing abnormal about the situation, stating that the A320 crew had misunderstood the vehicle's clearance – which had not been conditional on the aircraft's vacating first – and that the crew was unaware of Gatwick's standard runway inspection procedure.

But over the course of the year prior to the incident three other incursion events involving vehicles had taken place, and an internal probe by the airport's operations department highlighted several issues – including checks being carried out at "excessive speed", over 70mph (110km/h).

The probe determined that inspections were being performed "with the next arrival in mind rather than the task at hand", and while its recommendations included two reviews of inspection procedures, neither had been completed by the time of the Aer Lingus incident.

Gatwick has a declared runway capacity of 55 movements per hour and is seeking to increase this, the Air Accidents Investigation Branch states, although it points out that this is "not imposed" but set by the airport operator.

"Both [air traffic control] and the airside operations teams were striving to carry out runway inspections under the prevailing working environment," it says.

"There was, however, evidence of a lack of understanding of how each discipline’s work impacted on others operating at the airport and had potentially normalised procedures that would otherwise have been considered undesirable, or at worst unacceptable."

It adds that this meant the air traffic control probe "saw nothing wrong" in the Aer Lingus event, a view in "direct contrast" with the opinion of the airline and other carriers.

Although measures have since been drawn up to address a number of issues highlighted by the investigation, the inquiry says "many" of these "have yet to be completed".

"In setting the capacity [level] it is important to balance maximising the number of aircraft operating to the airport with the safety of the operation itself," it adds.

"This investigation indicates that the pressure of meeting the operating targets has had a direct effect on undertaking runway inspections both safely and effectively."