The RAF is trying to establish how a woman spent several months living at RAF Valley on Anglesey posing as a medical student.
Hawk jets fly from RAF Valley
The woman, a member of the Territorial Army (TA), posed as an army captain training to be a doctor.
She sat in on medical consultations and went on a training flight with the Sea King rescue helicopter squadron.
The woman also managed to remain undetected at RNAS Culdrose in Cornwall for four days before she was arrested.
The woman is no longer in possession of her TA identity card, and is the subject of an army investigation.
The RAF said she did not perform any patient examinations, nor go on any rescue operations with the Sea Kings.
The BBC understands that the RAF has sent 34 letters to patients who had medical consultations at Valley which the woman sat in on.
She remains a member of the TA, but has had her uniform taken away, along with her ID card.
Valley is one of the RAF's leading bases, and is home to the UK's only advanced training and tactics unit, in charge of training all air force and navy fast jet pilots.
The woman began posing as a trainee GP there in early October 2003, but she was found out in late February 2004 when she "transferred" to another base.
She was caught by civilian police, but no charges are to be brought against her.
The RAF also said the woman ran up a bill in the mess, although it could not confirm the amount. The bill has been paid, but the RAF did not know who settled it.
RAF Valley said it would not have an inquiry into the incident, although its security would be reviewed as a result.
Valley said it had "raised a number of issues as to what lessons can be learned" for all RAF bases.
Welsh Assembly Member for Ynys Mon Ieuan Wyn Jones said it raised serious issues at a time of heightened unease about terrorist attacks.
"I'm calling for the Ministry of Defence to conduct a full inquiry and for the findings to be made public," he said.