and pilot. To avoid these "G" forces, an FAA rule states, "use either a standardrate turn (SRT) or
30º AOB, whichever occurs first."
ANGLE OF BANK REQUIRED FOR A HALF AND FULL STANDARD RATE
TURN: CORRECTED FOR ALTITUDE
For BI, use the AOB for 15,000 feet, which is where the "10 percent
and 20 percent" rules originate. Assume standard day for all figures.
The turns are practiced initially in level flight, crosschecking the nose with VSI and altimeter and
the wings on the turn needle. A oneneedle width deflection produces a onehalf SRT and a
twoneedle deflection a full SRT. Checking for 30º in 10 seconds for a SRT will check the
performance of the turns on the RMI. Since the AOB required to produce a constantrate turn
will vary with airspeed, we need some method of determining proper bank for a specific needle
deflection. An accurate rule of thumb is to establish an AOB equal to 10% of the airspeed for a
onehalf SRT, i.e., at 150 KIAS, a 15º AOB should initially be established. Double the above
value for bank necessary in a full SRT. However, use 30º maximum AOB while flying
The above rule is known as the "10 percent" rule and is valid only during balanced flight. If
calibrated correctly, the turn needle always shows exact rate of turn even in an unbalanced
condition, but the AOB will vary according to the balance ball's position.
BASIC INSTRUMENTS FLIGHT PROCEDURES 3-13