A “power back” procedure is where reverse engine thrust is utilized to “back up” an aircraft in contrast to a “push back” where a vehicle is used to move the aircraft off of a gate. Utilizing a ground “marshaller” who directs the pilots, the aircraft thrust reversers are deployed and the engine throttles are advanced from idle.. As reverse thrust is increased, backward motion increases.
Since there is no way for the pilots to see what is behind them, the pilots are completely dependent on ground personnel to keep them from running into objects.
Using this procedure has a few serious associated hazards that generally limit its use generally to aircraft with tail mounted engines at airports which allow the procedure and at remote locations used as a last resort where suitable ground equipment is not available to “push back” the aircraft.
One of the major hazards is the risk of FOD or Foreign Object Damage (debris) to the engines and ground personnel. Prior to the late 1980’s the most widely produced passenger jet was the Boeing 727 followed by the DC-9 / MD80 series. Both of these aircraft have tail mounted engines that are elevated from the ground and less susceptible to ingesting objects littering the ramp areas. Since the 1990’s, the most widely produced aircraft have been the 737 series with 7467 produced (as of January 2013) followed by the Airbus 320 family of which 5635 have been produced as of June 2013 and these aircraft both have wing mounted engines that are positioned very close to the ground. Both the risk of engine ingestion with possible engine damage and flying objects propelled forward towards the terminal and ground personnel are real threats. Airport gate areas are often littered with items that fall off of passengers luggage such as zipper pulls, wheels, pull rings etc and even though most ramp personnel are instructed to monitor and pick up these items the “FOD walks” are generally done when the gate area is empty since most engine starts occur during or after the aircraft is pushed back and only run at idle.
I also speculate that since the tail mounted engines are much closer to the aircraft centerline than the wing mounted engines that the tail mounted engine aircraft are easier to control especially if there is any difference in the engines thrust. I speculate because I have never “powered back” a 737 or Airbus.
The risk of damage by collision with other aircraft or airport equipment is much higher when performing a power back primarily because the marshaller is standing in front of the aircraft using hand signals and maintaining visual contact with the flight deck and is unable to fully observe the area aft of the aircraft.
Many Airports have restrictions on aircraft using above idle power settings at the gate due to safety concerns of Jet Blast and noise. For example BWI (Baltimore, Washington International Thurgood Marshall) states in their tenant restrictions that ” Power backs exceeding a noise level of 120 dB, measured on the Airport terminal roof above the gate in question, shall not be authorized” and “Reverse-thrust power-back operations are prohibited at BWI Marshall between 2300 and 0700 local hours daily.”
Wear and tear on million dollar engines: The heat and stress on engines when using reverse thrust is higher. Also, the airflow is often disrupted increasing the chance for compressor stalls which require a Maintenance defect entry and usually a borescope inspection of the engine for internal damage to the compressor and HPT.
So, when airlines evaluate the risks outlined above they usually come to the conclusion that there is not enough economic advantage to be gained by allowing power backs. If they are allowed, they’re only permitted under the conditions outlined in the Air Carrier Flight and Operations manual and with prior approval from the airport authorities.
Today with the significantly increased focus on awareness of both safety and compliance in the Airline Industry I don’t think we’ll see very many “power backs” going forward. That’s a good thing in my opinion. In my world, the days of doing whatever it took to get the aircraft off the gate regardless of what the manual said to do are long gone.
Have any of you had the opportunity to power back either in the left seat or direct one from the ground? If so I’d love to hear your experiences. What Airports are powerbacks still utilized?