Staff at the BAE site in Samlesbury were evacuated this morning following reports of smoke.
Fire services were called to the site on Myerscough Smithy Road at around 6.45am on Monday November 13 after smoke was spotted coming out of a roof vent.
A spokesman for the fire service said: "We were called out to reports of smoke coming from a vent.
"Early reports suggest that this is not a major fire.
"No flames were visible."
Nobody is believed to have been injured in the incident.