Investigators have found no direct connection between the Boeing 787’s batteries and a fire on an Ethiopian Airlines Dreamliner at Heathrow on Friday.

The airport’s runways were shut for 90 minutes causing disruption to flights with some knock-on effects on Saturday when 42 flights were cancelled. Others were delayed although Heathrow reported average delays “of about 10 minutes”.

The UK Air Accidents Investigation Branch issued an early bulletin comfirming “extensive heat damage in the upper portion of the rear fuselage” of the Ethiopian Airlines 787 and said: “The initial investigation is likely to take several days.”

However, it noted: “It is clear that this heat damage is remote from the area in which the aircraft main and APU (Auxiliary Power Unit) batteries are located, and, at this stage, there is no evidence of a direct causal relationship.”

Ethiopian Airlines’ senior manager in the UK Mark Mangooni reported sparks having been seen coming from wires in an area that is part of the Dreamliner’s air conditioning system.

The carrier said its three other 787s would keep flying.

Ethiopian said the 787 had been parked for eight hours before smoke was spotted and the incident was “not related to flight safety”.

The aircraft was moved to a hangar at Heathrow while the investigation is carried out.

When the fire was spotted, fire-retardant foam was sprayed at the aircraft. The area on top of the fuselage in front of the tail appeared to be scorched.

The AAIB said the initial investigation was likely to take several days.

Meanwhile, Thomson Airways continued to fly two other Dreamliners after one was forced to return to Manchester airport on Friday as a “precautionary measure”.

The aircraft resumed service on Saturday after having a small number of components replaced.

“We want to reassure our customers that we have every confidence in this aircraft and would never operate it if we weren’t 100% sure of its safety,” a spokesman said.

All 50 Dreamliners in service worldwide were grounded at the start of the year following two separate incidents concerning its batteries.

Boeing modified the aircraft with new batteries and flights resumed in April.