If airplane A has 090 degrees set in the course selector, which instrument's VOR indications will it correspond to?

When airplane A has a course set at 090 degrees, it corresponds to a track heading that points directly towards the east. To understand which instrument’s VOR indications reflect this heading, it's essential to know how VOR (VHF Omnidirectional Range) systems work.

The VOR indicates a specific radial, which in this case is 090 degrees. This means airplane A is aligned to receive signals from a VOR station located on the 090-degree radial. Therefore, the appropriate instrument that displays the readings associated with a course selected at 090 degrees is Instrument 4.

Instrument 4 would effectively show the airplane A's position relative to the VOR station on the 090-degree heading, confirming that it is flying directly east. This alignment helps pilots navigate toward their intended waypoint effectively, showing the direct relationship between the course selector setting and the VOR indications on a specific instrument.

Thus, the answer is validated based on the fundamental principles of VOR navigation, which link the course selected to the corresponding instrument indications relevant to that specific radial.