Question

Which one of the following is the basic vertical reference in all forms of heading and attitude devices?

(a) Line perpendicular to artificial horizon

(b) Earth’s gravitational field

(c) Line perpendicular to actual horizon

(d) Earth’s magnetic field

This question was posed to me in an interview.

My question is taken from Vertical & Heading References topic in portion Air Data Systems, Altitude and Heading Reference of Avionics

Answer 1

Correct option is (b) Earth’s gravitational field

For explanation I would say: The basic vertical reference in all forms of heading and attitude reference devices is the Earth’s gravitational field. The direction of Earth’s gravitational field can be sensed with great accuracy in stationary systems. However, when the platform moves, all the instruments indicate the vector sum vehicle acceleration and local gravity.