What are aircraft ground instruments?

Question

What are aircraft ground instruments?

Answer 1

Never heard the term used that way.  Presumably the previous answerer was correct.  The term is an approximation for "ground-based navigational aids," meaning radio devices on the ground that provide data for electronic navigation devices in the airplane.

Answer 2

Depends how you mean.

Ground based aids are one form - these are generally radio beacons, and take on different forms dependent on their need - for example, DME measures distance with radar pulses, while VOR provides bearings and tracking to/from a site (usually those two are combined to provide both distance and bearing to a pilot).

Then there's the NDB - which is like a primitive VOR, giving directional guidance again.

Or the ILS - which provides a glideslope and path for the pilot to follow to the runway.

These are the only real ground instruments for a plane - the rest are in the plane itself!