 E models use the second seat for a weapon systems officer.Visibly, the F-15 has a unique feature" vis-à-vis "other modern fighter aircraft; it does not have the distinctive "turkey feather" aerodynamic exhaust petals covering its engine nozzles, because the petal design on the F-15 was problematic and could fall off in flight; therefore, they were removed, resulting in a 3% aerodynamic drag increase.A multimission avionics system includes a head-up display (HUD), advanced radar, AN/ASN-109 inertial guidance system, flight instruments, ultra high frequency communications, and tactical air navigation system and instrument landing system receivers.