With engines shutdown parking brake pressure bleeds off and allows aircraft to roll back on slope.

Attributes
ACN	301990
Time
Date	199504
Day	Tue
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : pit
State Reference	PA
Altitude	agl bound lower : 0 agl bound upper : 0
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	F28 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	ground : holding
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : flight engineer
Experience	flight time last 90 days : 150 flight time total : 7400 flight time type : 520
ASRS Report	301990
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : cfi pilot : commercial pilot : atp
Experience	flight time last 90 days : 150 flight time total : 11300 flight time type : 1400
ASRS Report	302120
Events
Anomaly	aircraft equipment problem : critical other anomaly other anomaly other
Independent Detector	other flight crewa
Resolutory Action	flight crew : overcame equipment problem
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

After a normal pushback from pit international terminal, we taxied out for takeoff. While taxiing we were given an ATC delay for takeoff of about 30 mins. Ground control then told us to pull into the runway 28R run-up pad. At the pad I then set the parking brake and shut down the #2 engine. Engine #1 was never started after pushback. We left the APU running to provide electric power and airconditioning. The time was XA05 when we shut down #2 engine. We both commented on not holding at this spot in yrs. We also discussed this sharp 'drop off' right behind the aircraft. After parking our nose was facing the taxiway and our tail point directly at the approximately 50 ft 'drop-off' behind us. In previous yrs I was a first officer on boeing 737-200 aircraft and we had parked at this point for ATC delays with engines shut down and experienced no problems. The holding pad is inclined down toward the drop-off! Then at about XA20 local time my first officer thought he heard the parking brake released but looked over at me and saw that my feet were on the floor and my seat was pulled back from a normal flight position. So he did not say anything to me because he thought the noise may have come from the galley. A few seconds alter I just happened to look outside. To my shock we were rolling backwards. I then slid forward and stepped on the toe brakes but nothing happened - no brakes and we were still rolling backwards toward the steep drop-off. I then grabbed the emergency brakes and the aircraft stopped. The first officer then turned on the electric hydraulic pumps (which are normally off) and built up the hydraulic press. I did not realize that the brakes would release by themselves even though the aircraft has a brake accumulator! This is a very dangerous situation because of this bleed down problem in the F-28's. I now know that other pilots have had the exact same thing happen to them. I suggest a new mandatory procedure be adopted, if engines are shut down and wheels are not chocked, electric boost pumps must be left on!! Otherwise a very serious accident will happen when someone rolls off a parking spot with an F-28 that has it's parking brake 'set.'

Original NASA ASRS Text

Title: WITH ENGS SHUTDOWN PARKING BRAKE PRESSURE BLEEDS OFF AND ALLOWS ACFT TO ROLL BACK ON SLOPE.

Narrative: AFTER A NORMAL PUSHBACK FROM PIT INTL TERMINAL, WE TAXIED OUT FOR TKOF. WHILE TAXIING WE WERE GIVEN AN ATC DELAY FOR TKOF OF ABOUT 30 MINS. GND CTL THEN TOLD US TO PULL INTO THE RWY 28R RUN-UP PAD. AT THE PAD I THEN SET THE PARKING BRAKE AND SHUT DOWN THE #2 ENG. ENG #1 WAS NEVER STARTED AFTER PUSHBACK. WE LEFT THE APU RUNNING TO PROVIDE ELECTRIC PWR AND AIRCONDITIONING. THE TIME WAS XA05 WHEN WE SHUT DOWN #2 ENG. WE BOTH COMMENTED ON NOT HOLDING AT THIS SPOT IN YRS. WE ALSO DISCUSSED THIS SHARP 'DROP OFF' RIGHT BEHIND THE ACFT. AFTER PARKING OUR NOSE WAS FACING THE TXWY AND OUR TAIL POINT DIRECTLY AT THE APPROX 50 FT 'DROP-OFF' BEHIND US. IN PREVIOUS YRS I WAS A FO ON BOEING 737-200 ACFT AND WE HAD PARKED AT THIS POINT FOR ATC DELAYS WITH ENGS SHUT DOWN AND EXPERIENCED NO PROBS. THE HOLDING PAD IS INCLINED DOWN TOWARD THE DROP-OFF! THEN AT ABOUT XA20 LCL TIME MY FO THOUGHT HE HEARD THE PARKING BRAKE RELEASED BUT LOOKED OVER AT ME AND SAW THAT MY FEET WERE ON THE FLOOR AND MY SEAT WAS PULLED BACK FROM A NORMAL FLT POS. SO HE DID NOT SAY ANYTHING TO ME BECAUSE HE THOUGHT THE NOISE MAY HAVE COME FROM THE GALLEY. A FEW SECONDS ALTER I JUST HAPPENED TO LOOK OUTSIDE. TO MY SHOCK WE WERE ROLLING BACKWARDS. I THEN SLID FORWARD AND STEPPED ON THE TOE BRAKES BUT NOTHING HAPPENED - NO BRAKES AND WE WERE STILL ROLLING BACKWARDS TOWARD THE STEEP DROP-OFF. I THEN GRABBED THE EMER BRAKES AND THE ACFT STOPPED. THE FO THEN TURNED ON THE ELECTRIC HYD PUMPS (WHICH ARE NORMALLY OFF) AND BUILT UP THE HYD PRESS. I DID NOT REALIZE THAT THE BRAKES WOULD RELEASE BY THEMSELVES EVEN THOUGH THE ACFT HAS A BRAKE ACCUMULATOR! THIS IS A VERY DANGEROUS SIT BECAUSE OF THIS BLEED DOWN PROB IN THE F-28'S. I NOW KNOW THAT OTHER PLTS HAVE HAD THE EXACT SAME THING HAPPEN TO THEM. I SUGGEST A NEW MANDATORY PROC BE ADOPTED, IF ENGS ARE SHUT DOWN AND WHEELS ARE NOT CHOCKED, ELECTRIC BOOST PUMPS MUST BE LEFT ON!! OTHERWISE A VERY SERIOUS ACCIDENT WILL HAPPEN WHEN SOMEONE ROLLS OFF A PARKING SPOT WITH AN F-28 THAT HAS IT'S PARKING BRAKE 'SET.'

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.