WASHINGTON, April 10 (Reuters) - The chair of the

National Transportation Safety Board (NTSB) said the loss of an

engine cover on a Southwest Airlines Boeing 737-800 on

Sunday that fell off during takeoff in Denver and struck the

wing flap was the result of a maintenance issue.

NTSB Chair Jennifer Homendy told reporters after a Senate

hearing the airplane had been in for maintenance the night

before the incident in which it lost the engine cowling.

The board opted not to open a formal investigation, Homendy

added.

Southwest Flight 3695 returned safely to Denver

International airport around 8:15 a.m. local time on Sunday and

was towed to the gate.