<< >> NASA ASRS Report 172737, March 1991

Pilot of small aircraft on IFR plan cleared to 5000' inadvertently disengaged his autoplt and aircraft descended to 4500' before recovery to 5000'.

Attributes
ACN	172737
Time
Date	199103
Day	Mon
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : mad airport : hfd
State Reference	CT
Altitude	msl bound lower : 4500 msl bound upper : 5000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	tracon : bdl
Operator	general aviation : personal
Make Model Name	Small Aircraft, Low Wing, 1 Eng, Fixed Gear
Flight Phase	cruise other descent other
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : private pilot : instrument
Experience	flight time last 90 days : 50 flight time total : 1000 flight time type : 800
ASRS Report	172737
Person 2
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : overshoot non adherence : clearance
Independent Detector	other other : unspecified cockpit
Resolutory Action	flight crew : returned to intended course or assigned course flight crew : regained aircraft control
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

I was at 9000' and told to descend and maintain 5000'. I was getting ready to begin my approach to hfd, so I set the altitude preselect and began my descent. At this point I switched over to listen to the ATIS for hfd. While copying the ATIS I hit a few bumps which disengaged the autoplt. Since I was busy with getting ready for the approach, I did not notice the autoplt disengage. The altitude preselect did not capture 5000'. I noticed when approximately at 4500' and immediately went back to 5000'. I could not have been below 5000' for more than 2 mins. Comment: autoplts are great, but don't stop scanning all INS just because it is clear out and no traffic in area.

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Original NASA ASRS Text

Title: PLT OF SMA ON IFR PLAN CLEARED TO 5000' INADVERTENTLY DISENGAGED HIS AUTOPLT AND ACFT DESCENDED TO 4500' BEFORE RECOVERY TO 5000'.

Narrative: I WAS AT 9000' AND TOLD TO DSND AND MAINTAIN 5000'. I WAS GETTING READY TO BEGIN MY APCH TO HFD, SO I SET THE ALT PRESELECT AND BEGAN MY DSNT. AT THIS POINT I SWITCHED OVER TO LISTEN TO THE ATIS FOR HFD. WHILE COPYING THE ATIS I HIT A FEW BUMPS WHICH DISENGAGED THE AUTOPLT. SINCE I WAS BUSY WITH GETTING READY FOR THE APCH, I DID NOT NOTICE THE AUTOPLT DISENGAGE. THE ALT PRESELECT DID NOT CAPTURE 5000'. I NOTICED WHEN APPROX AT 4500' AND IMMEDIATELY WENT BACK TO 5000'. I COULD NOT HAVE BEEN BELOW 5000' FOR MORE THAN 2 MINS. COMMENT: AUTOPLTS ARE GREAT, BUT DON'T STOP SCANNING ALL INS JUST BECAUSE IT IS CLR OUT AND NO TFC IN AREA.

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.