Investigators continue to examine the site of the fire aboard an Ethiopian Airlines Boeing 787 at Heathrow.

The Ethiopian Dreamliner was parked at a stand when smoke was reported on Friday. Both Heathrow runways were closed for about 90 minutes while firefighters attended. The airport returned to normal today.

A team from the UK Air Accidents Investigation Bureau (AAIB), part of the Department for Transport, are on the ground at Heathrow where they have been joined by a team from Boeing.

The US National Transportation Safety Board (NTSB) confirmed it will also send a representative to assist.

The NTSB led investigations into the fire aboard a Japan Airlines 787 at Boston’s Logan airport in January which led to the grounding of the Dreamliner fleet. The aircraft only returned to the sky in May.

There is speculation that one of the Ethiopian aircraft’s lithium-ion batteries may be the source of the fire.

If so, it would be hugely damaging to Boeing and the 787 programme since the batteries were the cause of both the Japan Airlines fire and an emergency landing by an ANA 787, also in January.

Boeing’s share price plunged on Friday before recovering somewhat amid speculation the batteries were not involved.

The aircraft’s auxiliary power unit would have been operating at the time. of the fire on Friday. Ethiopian Airlines said a problem had been identified in the aircraft’s air conditioning system and that maintenance staff had seen sparks but no flames.

A full investigation could take months, but investigators can be expected to issue a bulletin on their initial findings more quickly.

There appears nothing to link a technical issue on a Thomson Airways 787 to the Ethiopian fire. The Thomson aircraft turned back soon after take off from Manchester on Friday, but all three Thomson Dreamliners departed the UK as normal on Saturday.

Ethiopian Airlines said it also plans to operate its 787 fleet as normal. The carrier has four Dreamliners and said: “The incident at Heathrow was not related to flight safety.”

The Ethiopian 787 at the centre of Friday’s alarm at Heathrow had been parked for eight hours before smoke was spotted.

The lithium-ion batteries are key components of the Boeing 787 which is made largely from carbon-composite materials and much lighter and more fuel-efficient than existing aircraft.

Part of the reason is that hydraulic systems have been replaced by electrical systems, requiring considerably more wiring and greater battery power on the aircraft. This means technical issues are more likely to involve the power systems.

The batteries are used primarily on the ground to save fuel and to turn on aircraft systems. Lithium-ion batteries are both powerful and light. However, they can be prone to overheat.

US regulatory authorities signed off the technical fix for the Dreamliner batteries in April which Boeing hailed as a “comprehensive set of solutions”.

These include separation of the individual cells within each battery to lower the risk of overheating and encasing the batteries to prevent a fire spreading.

However, the cause of the fire aboard the Japan Airlines 787 has not been identified and may not be – hence the concern about this latest incident.

Rival manufacturer Airbus dropped plans to use lithium-ion batteries in its latest aircraft in light of Boeing’s problems, announcing it would revert to heavier traditional batteries instead.

Ethiopian Airlines was the first carrier to resume 787 flights in May following the aircraft’s grounding.