The attitude indicator

Navigation · Chapter 27 · DGCA CPL and ATPL

How to read pitch and bank off the horizon, the vertical gyro and vanes that hold it level, its take-off and turning errors, and the electric and standby horizons.

Remember

Bar moves, symbol fixed: bar below = nose up; bar tilts opposite to bank.
Earth gyro: vertical spin axis, two gimbals (inner lateral, outer fore-and-aft).
Air-driven: four pendulous vanes. Electric: mercury switches + torque motors; fast erection 120°/min.
Take-off: nose up, right wing low. Slowing: nose down, left wing low.
Turning: under, right, over, right (climb except at 360°). Standby: own gyro, own power.

How do you read pitch and bank off the horizon?

What it shows

In the cockpit • Top middle of the six: the attitude indicator, also called the artificial horizon. • It is a small picture of what is out of the window. In cloud it is all you have.
It matches the world • Look at the real horizon through the windscreen, and the one on the dial. • They tilt together. The dial never moves on the panel.
Level • Horizon line across the middle. The little aeroplane sits on it.
Nose up • Nose up: the horizon slides down. The little aeroplane sits above it. • The aeroplane is fixed to the case. It is the horizon that moves.
Bank right • Bank right: the horizon tilts the other way, just as out of the window. • The little aeroplane still has not moved.
Rolling into a turn • Watch the dial alone: the whole blue and brown face turns, marks and all. • These stay still: the case, the little aeroplane and the orange pointer at the top.
Read the bank • The mark under the orange pointer is your bank. Long marks: 30° and 60°. • Bank right: the big white wedge moves left, and a mark on the right comes under the pointer. • The A320's screen does it the other way: its scale stays and a small pointer moves.
Both • 20° left, nose down.

What gyro is inside, and how is it mounted?

An earth gyro

Open the case • Inside, a rotor spins with its axis straight up: an earth gyro. The white bar is fixed to it. • From your seat the case stays put, and the gyro and bar seem to tilt inside it, just as the horizon does on the dial.
Now step outside • Seen from outside, the truth shows: the aircraft and the case tilt. The rotor and bar never move. • That is the whole trick of this instrument.
Two rings let it • Inner ring: lets the aircraft pitch round it. • Outer ring: lets the aircraft roll round it.
Why the dial looks as it does • The bar is the gyro's. The orange aeroplane is the case's. • So the picture is honest: you see the aircraft tilt against something that does not.