In an interview with Hop-A-Jet pilot Anthony Donato, who is also an A&P mechanic with inspection authorization, and analysis of historical data, the NTSB has documented a hung start problem in the engines of the Bombardier Challenger 604 that lost power and crashed on Feb. 9, 2024, in Naples, Florida.
According to the NTSB docket, 25 days prior to the accident, “a series of hung engine starts were recorded by the FDR [flight data recorder]. There were 10 hung starts in total between the two engines, with one successful start on engine 1 occurring during these start attempts.”
The NTSB explained, “A hung start, also known as a hot start or stagnated start, is defined as a start attempt that experiences a light off but does not then successfully continue to a self-sustaining idle speed before engine ITT [interstage turbine temperature] exceeds the start redline. Hung starts may be caused by a variety of factors, including weak starter performance, premature starter deactivation, a degraded or damaged compressor, incorrect scheduling of bleeds or compressor variable geometry, or bad fuel.”
In comparing the hung starts to the FDR data from the accident, the NTSB wrote, “the engines’ fuel and ITT behavior during the event flight was consistent with the behavior of the engines during the hung start rollbacks.”
During the interview with NTSB investigators, Donato summarized his experiences with hung starts in the Challenger, including an online, audio-only meeting where the issue was discussed. He didn’t recall when that meeting occurred. “Then they asked what do you think, and I told them…based on what I know about this airplane and the mechanics of it and how the systems work…it’s going to be the fuel control unit, or it’s going to be the inlet guide vanes, and I was extremely adamant about that.
“And I still firmly believe it, especially my involvement with the dual hung start issue I had, and when it took place, and that was an extremely abnormal issue. Out of the 12,000-plus hours in the Challengers [that he had logged], from time to time, you might get a hung start. By the time you go back, the other one starts up. This here was…the right engine would never start after, I don’t know how many attempts, and the left engine, it took, oh, gosh, I don’t know, three, four attempts.
“Finally, it got started and…we’re thinking, all right, maybe it’s a bleed issue, so let’s try to do a cross-bleed with the operating engine…we still couldn’t get the right engine going. So that was a telltale sign to me, as a mechanic, saying this is extremely abnormal. And I left it like that, and dispatch told me to hop in another airplane, and I did, and I left. That’s where I left it. I left the keys with maintenance.”
After learning about the accident, in which the two pilots were killed, Donato told investigators, “I’m just a pilot, but I want to know for the sake of my friends that died why this happened. Is it related because of the dual hung starts? I don't know, but it’s kind of weird where the data that's been plotted with the flight data recorder shows this anomaly tracking the same thing regarding fuel flow…So, in my lifetime of flying Challengers since ’95…I’ve had a handful of hung starts where you accepted throughout the years…I guess this is like a common thing.”
Asked about Hop-A-Jet’s maintenance and troubleshooting of the hung start issue, Donato expressed concerns about the difficulty of finding a cause for a problem that is difficult to replicate. “How would you feel? You would feel like—I don’t have anything conclusive…Do I just mark it up as an electronic gremlin…This was not an electronic gremlin. There was nothing electronic about that system…So I just think personally, even though I was told—I wasn’t part of the troubleshooting, but they called [engine manufacturer] GE to get advice on it.
“They said change the fuel filters, check the fuel. They’re GE. That’s what their recommendation was. I personally have not reviewed anything else, so based on that, I think they went based on GE’s recommendation. That was it, so I don’t know…I wish I had that answer but, like I said, as a mechanic I thought maybe GE or maybe there would have been other discussion of like we need to do other things.
“But it was just…and the thing is the next day the plane starts up fine…And then the plane flew for two weeks, and all of a sudden this happened? But the ironic—the thing that’s the commonality is both engines. So I’ll take this to my grave. I firmly believe whatever happened to me on the ground [during] start, what happened to those two engines again. And, unfortunately, it was in flight.
“They went into a hung mode where the engines—when he was coming in, Ed was dirtying up the airplane to the point where his gear, flaps, full flaps, and then he started bringing the power up, and there was no power to get. There was no power, and the only thing that happened was the ITT just creeped up, and two spools kept going down. Everything was just opposite, which is normally what I get doing hung starts.
“Well, I…hope that they do find something conclusive because that’s the only way I think people—NTSB needs to present this to the rest of the Challenger industry, saying we have conclusive evidence that this is what we think happened. And it needs to be precautionary. Information needs to be sent out. And, personally, service bulletins don’t cut it. They don’t have teeth. Unless you issue a mandatory bulletin or AD that has some substance that mandates people doing this, a service bulletin doesn’t have teeth.”
Further questioning uncovered another Hop-A-Jet Challenger, a Model 605 that had hung start issues. First, the left engine wouldn’t start, and it was removed and sent to GE, and a loaner engine was installed. Then, after a successful start, the right engine suddenly experienced a hung start. So that engine was also removed and sent to GE.
“So now I have a 605 in maintenance with two engines off,” Donato said. “So that was that airplane. Then, through the course of all this, ever since the accident, there was a Challenger 650, I think it is, same engines. The previous—the crews that were flying that airplane for a while brought up, ‘Oh, yeah, we’ve been having hung starts on this engine too.’ Really? When were you going to tell people about this? Our maintenance director went through the roof. So they remove that engine. It’s sent out to GE.
“Now we’re having a rash of issues, so there has to be some type of—something needs to come where people look at this, like…what’s going on here? Is this an industry problem? Is it a local problem nature? We don't know.”