A small low wing cpr transport on a test flight lost hydraulic pressure and quantity. During gear positioning check, aircraft descended below assigned altitude.

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Attributes
ACN	605349
Time
Date	200401
Day	Thu
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	msl bound lower : 5500 msl bound upper : 6000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : zzz.tracon
Operator	general aviation : corporate
Make Model Name	Small Aircraft, Low Wing, 1 Eng, Fixed Gear
Operating Under FAR Part	Part 91
Flight Plan	IFR
Aircraft 2
Navigation In Use	ils localizer & glide slope : n/s
Flight Phase	descent : approach
Person 1
Affiliation	company : corporate
Function	oversight : supervisor
Qualification	pilot : instrument pilot : private
Experience	flight time last 90 days : 33 flight time total : 4800 flight time type : 2800
ASRS Report	605349
Person 2
Affiliation	other
Function	maintenance : technician observation : observer
Events
Anomaly	aircraft equipment problem : critical altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other
Independent Detector	atc equipment other atc equipment : mode c other controllera other flight crewa other flight crewb
Resolutory Action	controller : issued advisory flight crew : diverted to another airport none taken : detected after the fact
Consequence	other
Factors
Maintenance	performance deficiency : fault isolation
Supplementary
Problem Areas	Flight Crew Human Performance Maintenance Human Performance Aircraft Chart Or Publication
Primary Problem	Flight Crew Human Performance

Narrative:

While on +/-2 hour maintenance test flight regarding engine problems, had hydraulic line break and could not alter position of gear or flaps. But '3 green' indicated gear might be down. While trying to unravel the mystery of how that could be, realized we were not on ILS course as we were supposed to be. But we were below and out of clouds and mechanic and I tried to spot airport. Told tower we had problems, but were in 'clear' and trying to spot airport. We did spot airport and headed directly for it, but approach said we were not on ILS course and were now at 5500 ft, instead of 6000 ft. Sometime about there, I remembered to 'cancel' IFR and asked tower to verify wheels were down. They said it seemed so and we landed (no flaps). It turned out, on last maneuver prior to hydraulic failure, we had put gear down, and failure occurred immediately thereafter, so gear was stuck down, not up.

Original NASA ASRS Text

Title: A SMALL LOW WING CPR TRANSPORT ON A TEST FLT LOST HYD PRESSURE AND QUANTITY. DURING GEAR POSITIONING CHK, ACFT DSNDED BELOW ASSIGNED ALT.

Narrative: WHILE ON +/-2 HR MAINT TEST FLT REGARDING ENG PROBS, HAD HYD LINE BREAK AND COULD NOT ALTER POS OF GEAR OR FLAPS. BUT '3 GREEN' INDICATED GEAR MIGHT BE DOWN. WHILE TRYING TO UNRAVEL THE MYSTERY OF HOW THAT COULD BE, REALIZED WE WERE NOT ON ILS COURSE AS WE WERE SUPPOSED TO BE. BUT WE WERE BELOW AND OUT OF CLOUDS AND MECH AND I TRIED TO SPOT ARPT. TOLD TWR WE HAD PROBS, BUT WERE IN 'CLR' AND TRYING TO SPOT ARPT. WE DID SPOT ARPT AND HEADED DIRECTLY FOR IT, BUT APCH SAID WE WERE NOT ON ILS COURSE AND WERE NOW AT 5500 FT, INSTEAD OF 6000 FT. SOMETIME ABOUT THERE, I REMEMBERED TO 'CANCEL' IFR AND ASKED TWR TO VERIFY WHEELS WERE DOWN. THEY SAID IT SEEMED SO AND WE LANDED (NO FLAPS). IT TURNED OUT, ON LAST MANEUVER PRIOR TO HYD FAILURE, WE HAD PUT GEAR DOWN, AND FAILURE OCCURRED IMMEDIATELY THEREAFTER, SO GEAR WAS STUCK DOWN, NOT UP.

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.