From the Douglas Boeing 717 FCOM
(Not for Operational Use) 
Powerback
* The following limitations are applicable when the airplane is using reverse thrust for reverse taxi (power back):
Thrust reversers on both engines must be operative.
Ramp slope limit range is +1% to 2%.
Application of brakes while backing is prohibited.
Powerback is not authorized for winds higher than 25 knots, or when ice, snow, or slush is on the ramp or during periods of heavy rain.
And, executing the manoeuvre.
Copyright ©The Boeing Company.
PT.10.2 POWERBACK
General
The powerback maneuver can be an efficient means for the airplane to depart the gate and transition to the taxi phase. There are, however, several factors of safety and passenger comfort that must be considered before commencing the maneuver and during the maneuver itself. These considerations are as follows:
Flight and ground crew must have completed an appropriate powerback procedures training program.
Powerback can be performed only in approved ramp areas.
Thrust reversers on both engines must be operative.
Ramp must be clear of contamination.
There must be no more than moderate precipitation.
Use minimum reverse thrust required.
Do not use brakes while the airplane is moving rearward.
Both pilots should have their feet on the floor during the powerback maneuver.
Verify all personnel and equipment are clear of engines fore and aft prior to initiating movement of thrust levers.
Executing the Maneuver
Check that the FLAP/SLAT handle is in the UP/RET position and that ground crewman (or coordinator) is in position to maintain visual contact with Captain. Having received ground control clearance for powerback, Captain signals readiness to begin powerback with a flash of nosewheel light. Coordinator responds with all clear signal and commences rolling motion with both wands to indicate start of powerback. Captain releases parking brakes and ensures both pilots feet are on the floor. Captain applies reverse thrust to reverse idle detent and checks both engines in reverse thrust condition.
NOTE: To facilitate backward movement in some instances of tire flat spots, chocks, or ramp conditions, a few feet of forward taxi may be appropriate prior to applying reverse thrust. Use normal brakes to stop forward roll.
Apply reverse thrust as required to initiate movement. Once motion has commenced, reduce EPR to maintain a safe speed. If the speed is too fast, move one reverse thrust lever to forward thrust idle. If airplane does not move initially with maximum reverse EPR, discontinue powerback operation. Coordinator advises the speed of reverse taxi by varying the speed of wand(s) rotation. To signal a turn, coordinator points downward with his right or left hand. Downward pointing hand indicates direction the tail should move and direction the Captain should turn the nose gear steering wheel. When reverse taxi is complete, coordinator will give the come ahead signal. Captain should then place reverse thrust levers full down and apply forward thrust as required and transition to normal taxi.
Emergency Stop
If an emergency stop is required, coordinator will discontinue the rolling motion of the wands and immediately signal forward taxi. Captain should respond immediately by placing reverse levers full down and applying forward thrust as required.
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