Narrative:

My assignment on aug/tue/05 was to work aircraft X which returned to ZZZ from air carrier flight to japan (aircraft lost hydraulic system #4 quantity and had to return to field). The turnover I got was no evidence of hydraulic leaks with #4 air driven pump and engine driven pump area clean. Fuel samples were taken with no hydraulic fluid detected (fuel tanks contain heat exchangers for hydraulic system). A note of interest was #1 and #2 both indicating 1.15 on EICAS (115%). The B747's have a tendency for unwanted hydraulic system xfer from system #4 to both system #1 and system #2 every time the gear retracts (over several cycles). This was the course we were pursuing as the cause of the returned flight. After balancing hydraulic quantities and operating hydraulic system; we concluded the system were running isolated and apparently normal. Next course of action was to simulate takeoff. Gear pins were installed; clearance received and gear handle was placed to 'up' position while monitoring for fluid xfer. Aircraft nose went airborne and tail of aircraft settled onto the ground. Preliminary investigation indicates that the body gears weren't 'pinned' at the proper location. Apparently my partner and I both pinned a lightening hole -- which was also the same diameter as the gear pin hole. This mistaken identify caused the body gear to unlock and semi-retract causing the already fuel ladened tail heavy aircraft to further shift the center of gravity more aft resulting with the aircraft resting on its tail. Callback conversation with reporter revealed the following information: the reporter said the reason the landing gear was to be pressurized was the xfer of hydraulic fluid from system #4 to hydraulic system #1 and #2. The idea was that fluid was xferring at the hydraulic brake system select module when the gear was retracting and brakes were applied from the retract pressure lines to stop the spinning wheels. Pins were placed in the wing gear; body gear and nose gear. When the body gear was pinned; the pins were put into holes in the jury strut that appears to be the ground lock pin holes. The holes in fact were lightening holes drilled in the jury strut. When the gear handle was raised; the body gear retracted and the tail heavy airplane settled on the tail incurring major damage. After the in-house investigation and a campaign by engineering it was found the lightening holes in the jury strut on this airplane and only this airplane were drilled to allow ground lock ground pins to be inserted. No other B747 aircraft in the fleet was found with these holes allowing a gear pin to be installed.

Related reports:

Google
 

Original NASA ASRS Text

Title: A B747-400 WHILE TROUBLESHOOTING FOR #4 HYD FLUID XFER TO #1 AND #2 SYS. WITH MAIN AND NOSE GEAR PINNED HANDLE WAS RAISED AND BODY GEAR RETRACTED. AIRPLANE SETTLED ON TAIL INCURRING DAMAGE.

Narrative: MY ASSIGNMENT ON AUG/TUE/05 WAS TO WORK ACFT X WHICH RETURNED TO ZZZ FROM ACR FLT TO JAPAN (ACFT LOST HYD SYS #4 QUANTITY AND HAD TO RETURN TO FIELD). THE TURNOVER I GOT WAS NO EVIDENCE OF HYD LEAKS WITH #4 AIR DRIVEN PUMP AND ENG DRIVEN PUMP AREA CLEAN. FUEL SAMPLES WERE TAKEN WITH NO HYD FLUID DETECTED (FUEL TANKS CONTAIN HEAT EXCHANGERS FOR HYD SYS). A NOTE OF INTEREST WAS #1 AND #2 BOTH INDICATING 1.15 ON EICAS (115%). THE B747'S HAVE A TENDENCY FOR UNWANTED HYD SYS XFER FROM SYS #4 TO BOTH SYS #1 AND SYS #2 EVERY TIME THE GEAR RETRACTS (OVER SEVERAL CYCLES). THIS WAS THE COURSE WE WERE PURSUING AS THE CAUSE OF THE RETURNED FLT. AFTER BALANCING HYD QUANTITIES AND OPERATING HYD SYS; WE CONCLUDED THE SYS WERE RUNNING ISOLATED AND APPARENTLY NORMAL. NEXT COURSE OF ACTION WAS TO SIMULATE TKOF. GEAR PINS WERE INSTALLED; CLRNC RECEIVED AND GEAR HANDLE WAS PLACED TO 'UP' POS WHILE MONITORING FOR FLUID XFER. ACFT NOSE WENT AIRBORNE AND TAIL OF ACFT SETTLED ONTO THE GND. PRELIMINARY INVESTIGATION INDICATES THAT THE BODY GEARS WEREN'T 'PINNED' AT THE PROPER LOCATION. APPARENTLY MY PARTNER AND I BOTH PINNED A LIGHTENING HOLE -- WHICH WAS ALSO THE SAME DIAMETER AS THE GEAR PIN HOLE. THIS MISTAKEN IDENT CAUSED THE BODY GEAR TO UNLOCK AND SEMI-RETRACT CAUSING THE ALREADY FUEL LADENED TAIL HVY ACFT TO FURTHER SHIFT THE CTR OF GRAVITY MORE AFT RESULTING WITH THE ACFT RESTING ON ITS TAIL. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR SAID THE REASON THE LNDG GEAR WAS TO BE PRESSURIZED WAS THE XFER OF HYD FLUID FROM SYS #4 TO HYD SYS #1 AND #2. THE IDEA WAS THAT FLUID WAS XFERRING AT THE HYD BRAKE SYS SELECT MODULE WHEN THE GEAR WAS RETRACTING AND BRAKES WERE APPLIED FROM THE RETRACT PRESSURE LINES TO STOP THE SPINNING WHEELS. PINS WERE PLACED IN THE WING GEAR; BODY GEAR AND NOSE GEAR. WHEN THE BODY GEAR WAS PINNED; THE PINS WERE PUT INTO HOLES IN THE JURY STRUT THAT APPEARS TO BE THE GND LOCK PIN HOLES. THE HOLES IN FACT WERE LIGHTENING HOLES DRILLED IN THE JURY STRUT. WHEN THE GEAR HANDLE WAS RAISED; THE BODY GEAR RETRACTED AND THE TAIL HVY AIRPLANE SETTLED ON THE TAIL INCURRING MAJOR DAMAGE. AFTER THE IN-HOUSE INVESTIGATION AND A CAMPAIGN BY ENGINEERING IT WAS FOUND THE LIGHTENING HOLES IN THE JURY STRUT ON THIS AIRPLANE AND ONLY THIS AIRPLANE WERE DRILLED TO ALLOW GND LOCK GND PINS TO BE INSERTED. NO OTHER B747 ACFT IN THE FLEET WAS FOUND WITH THESE HOLES ALLOWING A GEAR PIN TO BE INSTALLED.

Data retrieved from NASA's ASRS site as of January 2009 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.