Refer to figures. 
An air driven attitude indicator uses a 'vertically tied' gyro to give a datum against which the roll and pitch attitude of an aircraft can be displayed. The gyro rotor is rotated anticlockwise, erected and maintained parallel with Earth horizontal using air from a vacuum pump attached to the aircraft engine. Due to the two methods (pendulous vanes and low centre of gravity) used to keep the gyroscope spin axis vertically tied, indication errors will occur when accelerating and decelerating. These errors are:

• Acceleration - Pitch up + roll right
• Deceleration - Pitch down + roll left

Pendulous Error (Roll):

To assist in keeping it erect the gyro assembly is designed to behave like a pendulum, in level unaccelerated flight it tends to remain vertical but any linear acceleration will cause the base of the gyro assembly to swing forwards or backwards. When the aircraft accelerates the base of the unit will swing towards the pilot, precession causes this force to be a applied at 90° in an anticlockwise direction so the gyro will tilt to the left. As the gyro is attached to the horizon bar the AI will therefore indicate a roll to the right.

Erection Error (Pitch):

Having spun up the rotor, air leaves the gyro case via 4 ports placed at 90° intervals at the bottom of the case. Each of these ports has a pendulous vane , pivoted at the top, which hangs down to cover half the port when the gyro is vertical. The purpose of the pendulous vanes is to keep the gyro erect. When the gyro is vertical the airflow out of each port is identical so the reaction forces cancel each other out. If the gyro wanders off the vertical some of the vanes will swing closed while others will swing open causing unequal air jets and a subsequent reaction. This reaction causes the gyro to precess back to the vertical.

Unfortunately this erection arrangement will give rise to errors when the aircraft accelerates or decelerates. Longitudinal acceleration will cause the lateral pendulous vanes to swing back causing an unbalanced sideways airflow which causes the gyro to precess in a direction 90° anticlockwise to the force. This causes the gyro assembly to tilt towards the pilot which lowers the horizon line and gives a false pitch up indication. The opposite occurs on deceleration.

erection error → INCORRECT.  Acceleration causes an erection error which gives a false pitch up indication but there's also a pendulous error which causes a false roll indication to the right.

a temporary error in both pitch and roll → CORRECT.  Acceleration causes false pitch up and roll right indications but these are temporary and only occur during acceleration.

apparent drift → INCORRECT.  The gyro is tied to the local vertical and does not experience apparent drift

a temporary error in pitch only → INCORRECT.  Acceleration causes temporary errors in pitch and roll