The thing that catches most people moving across is that AS9100 is not a standard you simply add to an existing certificate. Aerospace auditing sits inside the IAQG scheme, so the auditor requirements come from the AS9104 series and the authority to audit comes through a certification body approved under that scheme, with the auditor recorded in the aerospace database. That makes the more useful question which certification body you intend to audit for, because they will tell you precisely which training and which supervised aerospace audits they need before they can put you on a job.
I do not audit aerospace myself so take this as direction rather than detail. From what colleagues in that lane describe, your ISO 9001 lead auditor background covers the auditing skills but not the sector requirements, and the aerospace specific training plus supervised experience is the part nobody gets around. Worth asking here whether anyone has been through it recently, since scheme rules change more often than the standard does.
------------------------------
Dilawar Laghari
Auditor, Consultant and Trainer
AuditWorkshop.com
------------------------------