Narrative:

At approximately XA20L en route bro-iah the green system hydraulic low pressure light illuminated. The pressure dropped to '0' within 20 seconds. I asked the first officer to read the checklist for low pressure hydraulic from the QRH. We entered a holding pattern over psx during this time. We felt that there was a possibility that a low level light may have followed the illumination of the low pressure light. Due to my experience with having flown the ATR for over 6 yrs, the low pressure light is often followed by an illumination of the low level light, if the level reaches the triggering point of .67 gallons. Even though we had no steady illumination of the low level light, we treated it as a failure of the green hydraulic system. We planned to manually extend the gear. We did not declare an emergency. Callback conversation with reporter revealed the following information: the reporter stated the low pressure checklist calls for the green system to be deselected and the hydraulic xfeed opened which allows the blue system fluid to pressurize the green system. If there is a low fluid level light then the xfeed should not be opened. If it is open it should automatically close, protecting the good system fluid from being pumped overboard through the leak in the faulty system. In the reporter's case the low fluid light never did come on. The low pressure checklist was never completed to the point which calls for the hydraulic xfeed to be opened. The gear was lowered by the alternate method and the landing made. The reporter was unable to determine how much fluid was put in by the mechanics after landing. A few days later that airplane had further hydraulic problems. The low pressure light came on while the airplane was on the ground. There was no green system low level light. There was no fluid in the green system. The green system low level light should have been on. No one attempted to xfeed the blue system into the empty green system. With the aircraft not sensing the low level in the green system could all the good system have been pumped overboard? The reporter did not know. However, if the green system and the blue system fluid were gone, there would have been complete hydraulic failure. Braking would be from accumulators and only 6 applications. There would be no parking brakes, no nosewheel steering, no flaps or spoilers, and gear down by the alternate system.

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Original NASA ASRS Text

Title: THE GREEN HYD SYS LOW PRESSURE LIGHT CAME ON, HOWEVER THE LOW LEVEL LIGHT DID NOT COME ON. THE WRONG PROC WAS FOLLOWED. THE GEAR WAS LOWERED VIA THE ALTERNATE SYS AND THE BLUE HYD SYS XFEED WAS NOT OPENED.

Narrative: AT APPROX XA20L ENRTE BRO-IAH THE GREEN SYS HYD LOW PRESSURE LIGHT ILLUMINATED. THE PRESSURE DROPPED TO '0' WITHIN 20 SECONDS. I ASKED THE FO TO READ THE CHKLIST FOR LOW PRESSURE HYD FROM THE QRH. WE ENTERED A HOLDING PATTERN OVER PSX DURING THIS TIME. WE FELT THAT THERE WAS A POSSIBILITY THAT A LOW LEVEL LIGHT MAY HAVE FOLLOWED THE ILLUMINATION OF THE LOW PRESSURE LIGHT. DUE TO MY EXPERIENCE WITH HAVING FLOWN THE ATR FOR OVER 6 YRS, THE LOW PRESSURE LIGHT IS OFTEN FOLLOWED BY AN ILLUMINATION OF THE LOW LEVEL LIGHT, IF THE LEVEL REACHES THE TRIGGERING POINT OF .67 GALLONS. EVEN THOUGH WE HAD NO STEADY ILLUMINATION OF THE LOW LEVEL LIGHT, WE TREATED IT AS A FAILURE OF THE GREEN HYD SYS. WE PLANNED TO MANUALLY EXTEND THE GEAR. WE DID NOT DECLARE AN EMER. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE LOW PRESSURE CHKLIST CALLS FOR THE GREEN SYS TO BE DESELECTED AND THE HYD XFEED OPENED WHICH ALLOWS THE BLUE SYS FLUID TO PRESSURIZE THE GREEN SYS. IF THERE IS A LOW FLUID LEVEL LIGHT THEN THE XFEED SHOULD NOT BE OPENED. IF IT IS OPEN IT SHOULD AUTOMATICALLY CLOSE, PROTECTING THE GOOD SYS FLUID FROM BEING PUMPED OVERBOARD THROUGH THE LEAK IN THE FAULTY SYS. IN THE RPTR'S CASE THE LOW FLUID LIGHT NEVER DID COME ON. THE LOW PRESSURE CHKLIST WAS NEVER COMPLETED TO THE POINT WHICH CALLS FOR THE HYD XFEED TO BE OPENED. THE GEAR WAS LOWERED BY THE ALTERNATE METHOD AND THE LNDG MADE. THE RPTR WAS UNABLE TO DETERMINE HOW MUCH FLUID WAS PUT IN BY THE MECHS AFTER LNDG. A FEW DAYS LATER THAT AIRPLANE HAD FURTHER HYD PROBS. THE LOW PRESSURE LIGHT CAME ON WHILE THE AIRPLANE WAS ON THE GND. THERE WAS NO GREEN SYS LOW LEVEL LIGHT. THERE WAS NO FLUID IN THE GREEN SYS. THE GREEN SYS LOW LEVEL LIGHT SHOULD HAVE BEEN ON. NO ONE ATTEMPTED TO XFEED THE BLUE SYS INTO THE EMPTY GREEN SYS. WITH THE ACFT NOT SENSING THE LOW LEVEL IN THE GREEN SYS COULD ALL THE GOOD SYS HAVE BEEN PUMPED OVERBOARD? THE RPTR DID NOT KNOW. HOWEVER, IF THE GREEN SYS AND THE BLUE SYS FLUID WERE GONE, THERE WOULD HAVE BEEN COMPLETE HYD FAILURE. BRAKING WOULD BE FROM ACCUMULATORS AND ONLY 6 APPLICATIONS. THERE WOULD BE NO PARKING BRAKES, NO NOSEWHEEL STEERING, NO FLAPS OR SPOILERS, AND GEAR DOWN BY THE ALTERNATE SYS.

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.