A fire aboard an empty 787 Dreamliner at Heathrow Airport spooked Boeing investors Friday, as they feared the reemergence of battery problems that grounded the plane for months earlier this year.

Boeing shares fell $5.01, or 4.7 percent, to $101.87. At its peak, the selling knocked off $7.89 a share, or $6 billion of market value. The stock recovered slightly as speculation about the cause of the fire shifted away from the batteries.

The cause of the fire on the Ethiopian Airlines plane — which broke out more than eight hours after the plane landed in London — remained under investigation. The location of the fire led some experts to surmise that the cause was not the plane’s lithium-ion batteries.

Also Friday, an unspecified mechanical issue caused another 787 flown by Thomson Airways to return to Manchester, England, adding to concerns about the plane.

Runways at Heathrow were shut down for nearly an hour as emergency crews put out the fire. No passengers were on the plane.

The 787 was grounded in January following two incidents with its lithium-ion batteries. One 787 caught fire shortly after it landed at Boston’s Logan International Airport on Jan. 7. Boeing marketed the plane to airlines as a revolutionary jet that — thanks to its lightweight design — burns 20 percent less fuel than comparable aircraft. Boeing has delivered 66 of the planes to customers, with another 864 of them on order.

Boeing’s stock partly rebounded after photos were circulated showing the section of the plane damaged by the fire — an area far away from the battery compartment.

The photos show the rear roof of the plane burned, near the jet’s vertical stabilizer, often called the tail. The batteries are in two separate compartments under the floor of the plane. One is near the wings; the other is under the cockpit.

“Evidence thus far suggests that the battery was not the cause of the fire at Heathrow,” Jason Gursky, an aerospace analyst with Citi, told investors. “The images out of London are not consistent with the fire at Boston Logan, which prompted the grounding earlier this year.”

There were also few details provided about the severity of the Thomson Airways incident. The jet had taken off from Manchester headed to an airport in Sanford, Fla., near Orlando. The airline said it returned to Manchester “as a precautionary measure.” All 291 passengers disembarked safely, and engineers inspected the aircraft, the airline said.

— Reuters