<< >> NASA ASRS Report 335819, May 1996

While looking for traffic during the climb, a LR35 flight crew overshot their assigned altitude. The sun's glare caused the altitude hold to appear illuminated and selected when it was not, and as a result, the autoplt did not capture the altitude.

Attributes
ACN	335819
Time
Date	199605
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : ags
State Reference	GA
Altitude	msl bound lower : 19000 msl bound upper : 19500
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zjx tower : dtw
Operator	general aviation : corporate
Make Model Name	Learjet 35
Operating Under FAR Part	Part 91
Flight Phase	climbout : intermediate altitude
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 101 flight time total : 8340 flight time type : 1000
ASRS Report	335819
Person 2
Affiliation	Other
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 150 flight time total : 1500 flight time type : 700
ASRS Report	336120
Events
Anomaly	altitude deviation : overshoot non adherence : clearance
Independent Detector	other controllera other flight crewa
Resolutory Action	flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Cleared to FL190 during climb. Approaching FL190, ATC called TA. While looking outside for traffic, autoplt did not hold altitude at FL190. When I noted the altimeter again, I saw it climbing above FL190. I immediately stopped climb and returned to FL190 after FL195. I believe that glare from sunlight gives a false indication on altitude hold annunciator. Altitude hold function can appear to be on when it is not. Future prevention actions: be on lookout for sunlight glare causing false annunciator indications, and ensure proper internal illumination of the altitude hold annunciator. Also, I will be especially careful as to altitude control when distracted by ATC and looking outside of cockpit for traffic. Supplemental information from acn 336120: ATC called us about the altitude after the altitude was back at about FL190. We never saw any traffic nearby and do not know of any conflict.

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Original NASA ASRS Text

Title: WHILE LOOKING FOR TFC DURING THE CLB, A LR35 FLC OVERSHOT THEIR ASSIGNED ALT. THE SUN'S GLARE CAUSED THE ALT HOLD TO APPEAR ILLUMINATED AND SELECTED WHEN IT WAS NOT, AND AS A RESULT, THE AUTOPLT DID NOT CAPTURE THE ALT.

Narrative: CLRED TO FL190 DURING CLB. APCHING FL190, ATC CALLED TA. WHILE LOOKING OUTSIDE FOR TFC, AUTOPLT DID NOT HOLD ALT AT FL190. WHEN I NOTED THE ALTIMETER AGAIN, I SAW IT CLBING ABOVE FL190. I IMMEDIATELY STOPPED CLB AND RETURNED TO FL190 AFTER FL195. I BELIEVE THAT GLARE FROM SUNLIGHT GIVES A FALSE INDICATION ON ALT HOLD ANNUNCIATOR. ALT HOLD FUNCTION CAN APPEAR TO BE ON WHEN IT IS NOT. FUTURE PREVENTION ACTIONS: BE ON LOOKOUT FOR SUNLIGHT GLARE CAUSING FALSE ANNUNCIATOR INDICATIONS, AND ENSURE PROPER INTERNAL ILLUMINATION OF THE ALT HOLD ANNUNCIATOR. ALSO, I WILL BE ESPECIALLY CAREFUL AS TO ALT CTL WHEN DISTRACTED BY ATC AND LOOKING OUTSIDE OF COCKPIT FOR TFC. SUPPLEMENTAL INFO FROM ACN 336120: ATC CALLED US ABOUT THE ALT AFTER THE ALT WAS BACK AT ABOUT FL190. WE NEVER SAW ANY TFC NEARBY AND DO NOT KNOW OF ANY CONFLICT.

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.