Question

Which one of the following is not a navigation mode used by FMS for computing position of the aircraft?

(a) Inertial (IRS) – GPS

(b) Inertial (IRS) – DME/DME

(c) Inertial (IRS) – VOR/DME

(d) GPS only

I got this question in an international level competition.

Question is taken from Flight Management Systems topic in chapter Autopilots and Flight Management Systems of Avionics

Answer 1

Correct answer is (d) GPS only

The explanation is: Each FMS computes the aircraft position and the position accuracy. The FMS computed position is an optimum combination of the inertial position and the GPS or radio position, depending on which equipment provides the most accurate data. This results in four navigation modes: Inertial (IRS) – GPS, Inertial (IRS) – DME/DME, Inertial (IRS) – VOR/DME, Inertial (IRS) only. The only GPS is not used as the position information is within a radius where the aircraft is flying.