A fire on an empty Boeing 787 Dreamliner forced Heathrow Airport in London to temporarily close both its runways Friday.

There were no passengers on board the Ethiopian Airlines jetliner. Heathrow reports the aircraft was parked in an area away from the terminals and the suspension of incoming and outgoing flights is standard if fire crews are occupied with an incident.

Television images showed nearly a dozen fire trucks on the scene at Heathrow and firefighters standing around the Ethiopian Airlines plane. Fire-retardant foam appeared to have been sprayed, and it was not immediately clear if there was damage to the plane.

Boeing tweeted that they are aware of the incident and have Boeing personnel there.

“We’re working to fully understand and address this,” Boeing said.

British police said the fire aboard the plane is being treated as unexplained.

The National Transportation Safety Board said they are sending an accredited representative to London-Heathrow to assist in the investigation.

The 787, which Boeing calls the Dreamliner, is under unusual scrutiny because it was grounded worldwide for four months after lithium-ion batteries overheated on two of the jets. One caught fire at Boston’s Logan airport.

The planes resumed flying in April after Boeing made redesigns to the battery system that were approved by global aviation regulators. Ethiopian was the first airline to resume using the 787.

The Dreamliner is Boeing’s most technologically advanced airliner, with lightweight materials and other innovations designed to boost fuel efficiency. The fuel efficiency makes it suited for long flights including international routes.

The 787 is assembled at Boeing plants in Everett and North Charleston, S.C.

Shares of Boeing dropped almost 5 percent Friday after an empty 787 experienced a fire at Heathrow Airport.

Boeing shares fell $5.01, or 4.7 percent, to $101.87 in trading Friday. The shares earlier dropped as low as $98.99.

Shares of Boeing suppliers also fell. Precision Castparts fell $3.49, or 1.5 percent, to $233.78. Spirit Aerosystems, which also makes parts for the 787, fell 48 cents, or 2.1 percent, to $22.65.

Another Boeing 787 reportedly also experienced a tech issue on Friday.

Thomson Airways says one of its Boeing 787 Dreamliner planes traveling from England to the U.S. had to turn back after experiencing a technical issue.

Thomson said that flight 126 traveling from Manchester Airport to Sanford, Florida had returned to Manchester “as a precautionary measure.”

It said all passengers had disembarked from the plane and engineers are inspecting the aircraft.

The Associated Press contributed to this report.