As an Air Force E-11A battlefield communications aircraft conducted missions over Ghazni Province, Afghanistan, on Jan. 27, 2020, a fan blade broke inside the left engine. Efforts to address the problem led to a series of missteps that caused the aircraft to crash, killing the two pilots, according to a new Accident Investigation Board report.
The report, released Thursday by Air Combat Command, concluded that the broken blade caused the left engine to shut down automatically. But the pilots improperly assessed "that the right engine had failed or been damaged" and initiated right engine shutdown procedures, it adds.
With the right engine shut down, the pilots were in a "dual engine out emergency." They were unable to restart the right engine, though the report does not explain why. It's possible they attempted to restart the left instead, it states.
Lt. Col. Paul K. Voss, 46, and Capt. Ryan S. Phaneuf, 30, were killed in the crash. They were both assigned to the 430th Expeditionary Electronic Combat Squadron at Kandahar Airfield, and were on a qualification flight while conducting a combat sortie, the report states. The redacted investigation does not cite names, but Air Force Magazine identified Voss as the flight commander, with Phaneuf presumably the copilot.
The aircraft, tail number 11-9358, was being used as a Battlefield Airborne Communications Node, or BACN, acting as a "Wi-Fi in the sky" to boost other pilots' situational awareness of beyond-line-of-sight activity. BACN-equipped E-11 aircraft began operating in Afghanistan in 2011, according to the Air Force.
The engine fan malfunction occurred just before 1 p.m. local time, about an hour and 45 minutes into the flight, the report states.
The plane was in range to glide to and land at either Kabul International Airport in eastern Afghanistan, 17 nautical miles away, or Bagram Airfield, 38 nautical miles away, it adds.
At one point, the pilots could have glided to Forward Operating Base Shank -- 28 nautical miles away -- but had only an eight-minute window to begin that maneuver, the report states.
Instead, the crew, flying at about 41,000 feet, decided to initiate an airstart on the right engine and head toward Kandahar Airfield -- 230 nautical miles southwest from their position. An airstart uses the aircraft's airspeed to turn the engine turbines, a move that would require the aircraft to travel at 258 knots. The aircraft, a modified Bombardier Global Express BD-700, can reach a max speed of about 505 knots.
"... Mayday, Mayday, Mayday … it looks like we have an engine failure on both motors. We are proceeding direct to Kandahar at this time," one of the pilots is heard radioing to Air Traffic Control, per the report.
However, the aircraft was outside of the gliding distance to reach Kandahar; instead, the pilots tried maneuvering toward Forward Operating Base Sharana, about 217 nautical miles to the east of Kandahar. But it crashed in a field 21 nautical miles short of Sharana.
There is limited data on how the pilots reacted during the events, officials said. The harsh vibrations caused by the left engine malfunction stopped the Cockpit Voice Recorder, or CVR.
"Without the CVR, it is difficult to fully assess the human factors and understand why certain decisions were made," the report states.
Another key instrument, the digital flight data recorder, stopped recording because of the dual engine generator loss. While investigators could not confirm that an engine airstart was attempted, there were signs that suggested the pilots did try the reset, they said.
Because there was no digital flight recorder data to make clear the pilots' steps, it is possible they attempted to restart the left engine, thinking the right engine was the one malfunctioning, the report states. The pilots "may have concluded that the right engine suffered damage and therefore only elected to airstart the left engine," it says.
Following the E-11A single engine procedures checklist, the crew would have delayed starting the Auxiliary Power Unit, or APU, which would have offered electrical power to the engine.
But according to photographs taken of the crash site wreckage, the APU intake door was open, meaning that the crew "likely later used [it] in an attempted [auto turbine]-assisted airstart."
On first approach, search-and-rescue aircraft were unable to reach the crash site due to weather. Crews that were able to reach the wreckage the next day and were able to recover Voss and Phaneuf’s remains and some equipment, including the CVR and flight data recorder. The remaining wreckage was ultimately destroyed by U.S. forces, officials said at the time.
Ghazni Province has been under majority Taliban control since 2015, shortly after U.S. combat forces began drawing down in Afghanistan, but U.S. officials determined early on that the crash was not the result of enemy action.
It was not immediately clear how the crew misidentified the problem engine. In the first few moments, the crew alert system "did not directly indicate the left engine failure," the report states.
The Accident Investigation Board president, Brig. Gen. Craig Baker, found that the pilots had roughly a minute to deduce what was going on, but reacted just 24 seconds from the start of the violent vibrations to shut down the right engine.
Based on the information available, Baker concluded that the crew misidentified which engine suffered the failure, resulting in them shutting down the wrong one.
"I also find, by a preponderance of the evidence, that the [crew's] failure to airstart the right engine and their decision to recover the [aircraft] to [Kandahar] substantially contributed to the mishap," he said.
The aircraft, a Bombardier Global Express, was maintained by Northrop Grumman, which developed the BACN equipment. Northrop conducted the plane's last major inspection on Jan. 13, just two weeks before the accident. A final inspection was conducted one day prior to the flight, but "no aircraft discrepancies [were] identified," the Accident Investigation Board report states.
The report did not give a reason for the blade damage in the left engine, which was manufactured by Rolls-Royce.
The loss of the plane and its equipment was estimated at $120 million, the Air Force said in an accompanying release.
Editor's note: This article has been updated to correct the speed needed to perform an airstart.