<< >> NASA ASRS Report 308686, June 1995

Altitude deviation altitude excursion -- helicopter in automatic cruise mode climbs above the assigned altitude. Pilot recovers and autoplt is found to be faulty.

Attributes
ACN	308686
Time
Date	199506
Day	Mon
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : zzz
State Reference	US
Altitude	msl bound lower : 5000 msl bound upper : 5400
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	tracon : zzz
Operator	common carrier : air taxi
Make Model Name	Helicopter
Operating Under FAR Part	Part 135
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : commercial pilot : instrument
Experience	flight time last 90 days : 50 flight time total : 4100 flight time type : 100
ASRS Report	308686
Person 2
Affiliation	government : faa
Function	controller : departure
Qualification	controller : radar
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	other flight crewa
Resolutory Action	flight crew : overcame equipment problem flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

After establishing the aircraft in an autoplt held cruise condition ie, coupled to navigation, altitude and airspeed hold. I was occupied in the cockpit checking upcoming VOR, airport and ATIS frequencys. On looking up after a short period of time I noticed the aircraft was established in a 300 FPM rate of climb and the altitude was now 5400 ft MSL, 400 ft above flight planned cruise. I disengaged the coupled functions, descended to 5000 ft and carried out some functional checks on the autoplt. I ascertained that the higher level functions of the 4 axis autoplt were not reliable, but by restricting the use of the coupled functions to navigation and altitude hold, the system worked, and the flight was completed without further incident.

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Original NASA ASRS Text

Title: ALTDEV ALT EXCURSION -- HELI IN AUTO CRUISE MODE CLBS ABOVE THE ASSIGNED ALT. PLT RECOVERS AND AUTOPLT IS FOUND TO BE FAULTY.

Narrative: AFTER ESTABLISHING THE ACFT IN AN AUTOPLT HELD CRUISE CONDITION IE, COUPLED TO NAV, ALT AND AIRSPD HOLD. I WAS OCCUPIED IN THE COCKPIT CHKING UPCOMING VOR, ARPT AND ATIS FREQS. ON LOOKING UP AFTER A SHORT PERIOD OF TIME I NOTICED THE ACFT WAS ESTABLISHED IN A 300 FPM RATE OF CLB AND THE ALT WAS NOW 5400 FT MSL, 400 FT ABOVE FLT PLANNED CRUISE. I DISENGAGED THE COUPLED FUNCTIONS, DSNDED TO 5000 FT AND CARRIED OUT SOME FUNCTIONAL CHKS ON THE AUTOPLT. I ASCERTAINED THAT THE HIGHER LEVEL FUNCTIONS OF THE 4 AXIS AUTOPLT WERE NOT RELIABLE, BUT BY RESTRICTING THE USE OF THE COUPLED FUNCTIONS TO NAV AND ALT HOLD, THE SYS WORKED, AND THE FLT WAS COMPLETED WITHOUT FURTHER INCIDENT.

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.