An engine failure caused damage on 21 December to five E-8C JSTARS aircraft, or nearly one-third of the fleet of aerial ground surveillance aircraft, the US Air Force says.

Three of the five damaged aircraft returned to flight status at Warner Robins AFB, Georgia within three days, and a fourth aircraft is expected to be repaired shortly after the New Year’s Day, says the 116th Air Control Wing. The status of the fifth aircraft with the failed engine was not immediately available, but it appears to remain grounded.

The incident caused no damage to any of the Northrop APY-7 radars installed inside a belly canoe fairing on each of the JSTARS aircraft, a spokesman for the 116th Wing tells FlightGlobal.

The incident on 21 December is now under review by a Safety Investigation Board, the Air Force says.

Each E-8C -- a modified Boeing 707-300 -- is powered by four Pratt & Whitney TF33-102C engines, a 1950s design derived from the once ubiquitous P&W JT-3.

The engine failed during a maintenance test run on a crowded ramp by the runway, spewing debris from the engine around the ramp and parking areas.

Four airmen were evaluated for injuries but released. The 116th Wing grounded JSTARS flight operations briefly to clear debris from the failed engine off the airport.

Despite the damage caused to five of the 16 operationally-coded JSTARS aircraft, the air force says that there was no disruption to surveillance flights requested by field commanders.

“Our maintenance personnel are phenomenal,” says Col Thomas Grabowski, 116th Air Control Wing commander. “Their ability to restore these aircraft to flight status in such a short period of time demonstrates the combat mission ready posture of this unique organization.”

The incident occurs as top Air Force leaders consider whether to cancel a competition to select a business jet platform to replace the E-8C fleet. Another option under review is to re-start the competition in the future using a platform that could survive in contested airspace.