By Allison Lampert
(Reuters) - General Dynamics Corp's Gulfstream Aerospace has notified owners of its G500 and G600 jets and the Federal Aviation Administration that it has discovered soot at the rear of some of those business jets, possibly because of the way a small engine vents gas in flight.
The FAA and Gulfstream both said they did not consider the issue to be a safety risk.
Gulfstream told plane owners, in a previously unreported letter to operators of the G500 dated Nov 8 and reviewed by Reuters, that it would have a plan for a fix ready early next year after testing.
"While it is not a safety-of-flight issue, we are working with Gulfstream to ensure the company addresses it," the FAA told Reuters.
In its letter to operators of the G500, a large-cabin jet which entered service in 2018, Gulfstream said it had found soot build up on the inside of the aircraft skin and the frame near the auxiliary power unit (APU) – a small engine at the tail of the plane installed for supplementary power.
The company said in the maintenance letter that in some cases planes would need to have structural components replaced due to "no allowance for localized overheating."
Gulfstream, however, said in the letter the presence of soot was not necessarily "indicative of an overheat condition," but that if components needed to be replaced "additional aircraft downtime may be required."
It was not immediately clear how many planes might require those repairs.
Business jet makers have seen strong demand from wealthy buyers and companies who opted to fly private during the height of COVID-19.
While Gulfstream did not disclose a specific explanation, material from a company presentation and a source familiar with the matter said it's likely due to APU exhaust gases getting pushed through a structural gap and leaving soot deposits.
"We have investigated soot on the G500 and G600 aircraft, believe we know the cause, and are testing and validating our conclusions," Gulfstream said in an emailed statement, adding that the "appearance of soot in and around the APU exhaust is not abnormal."
Savannah, Georgia-based Gulfstream is the market leader by value of deliveries against large-cabin rivals Bombardier of Canada and France's Dassault. Parent General Dynamics has seen its aerospace unit backlog swell to $19.1 billion during the third quarter.
Gulfstream said it did not anticipate any restrictions on the use of the APU, which generates energy for functions like starting power for the main engines.
Gulfstream said it has "notified the FAA and are working collaboratively with them on this issue."
(Reporting By Allison Lampert in Montreal. Editing by Kevin Krolicki in Singapore and Nick Zieminski in New York)