Altitude deviation on descent due to wrong altimeter setting on captain's side.

Attributes
ACN	275151
Time
Date	199406
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : atr
State Reference	DE
Altitude	msl bound lower : 11000 msl bound upper : 11000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	Fokker 100
Operating Under FAR Part	Part 121
Flight Phase	descent other
Route In Use	enroute airway : dca
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial pilot : atp pilot : flight engineer
Experience	flight time last 90 days : 150 flight time total : 5500 flight time type : 1200
ASRS Report	275151
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : less severe other anomaly other
Independent Detector	other controllera
Resolutory Action	flight crew : overcame equipment problem
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

FK100 aircraft with EFIS in descent to cross bilit intersection at 11000 ft for dca. Approach questioned altitude. Captain side showed 11750 ft descending and 3 NM from bilit. My side (first officer) showed 900 ft higher. Captain leveled at 11000 ft on his altimeter, crosschecked both altimeter settings and captain's was set at 28- 29 not 29-80 as it should have read. Captain then leveled at 11000 ft and was then given further descent. I am sure that 29.80 had been set in both LCD windows. Also the previous altimeter setting was 29.78 which would only require a slight turn of the knob. On the ground we turned the knob to see how much you would have to turn it to reach from 29.80 to 28.90 and it took about 5-6 full spins of the knob. We both feel that this was not the cause, but that the LCD changed or skipped from a 9 to an 8. There was no traffic conflict in crossing bilit 1000 ft high and the captain did report the problem to maintenance in dca. Callback conversation with reporter revealed the following information: flight crew had aircraft change after this incident and were not able to follow up at the time. Reporter states that captain called dispatch at end of day to determine what maintenance had found. Apparently they could find nothing abnormal. Distressing to flight crew as they had tried to recreate the condition and one would have to turn too many revolutions to not be aware of the extreme setting change. Reporter has experienced such glitches of the led switching to the next digit inadvertently but never with the altimeter. He has not heard of this happening to any other flight crew or any other aircraft. This aircraft is equipped with a system whereby one pushes a button when FL180 on climb or descent to reset the altimeter to setting placed in lower area. This setting is part of the descent checklist and flight crew knows they placed correct setting because other altimeter and standby altimeter had the correct numbers.

Original NASA ASRS Text

Title: ALTDEV ON DSCNT DUE TO WRONG ALTIMETER SETTING ON CAPT'S SIDE.

Narrative: FK100 ACFT WITH EFIS IN DSCNT TO CROSS BILIT INTXN AT 11000 FT FOR DCA. APCH QUESTIONED ALT. CAPT SIDE SHOWED 11750 FT DSNDING AND 3 NM FROM BILIT. MY SIDE (FO) SHOWED 900 FT HIGHER. CAPT LEVELED AT 11000 FT ON HIS ALTIMETER, XCHKED BOTH ALTIMETER SETTINGS AND CAPT'S WAS SET AT 28- 29 NOT 29-80 AS IT SHOULD HAVE READ. CAPT THEN LEVELED AT 11000 FT AND WAS THEN GIVEN FURTHER DSCNT. I AM SURE THAT 29.80 HAD BEEN SET IN BOTH LCD WINDOWS. ALSO THE PREVIOUS ALTIMETER SETTING WAS 29.78 WHICH WOULD ONLY REQUIRE A SLIGHT TURN OF THE KNOB. ON THE GND WE TURNED THE KNOB TO SEE HOW MUCH YOU WOULD HAVE TO TURN IT TO REACH FROM 29.80 TO 28.90 AND IT TOOK ABOUT 5-6 FULL SPINS OF THE KNOB. WE BOTH FEEL THAT THIS WAS NOT THE CAUSE, BUT THAT THE LCD CHANGED OR SKIPPED FROM A 9 TO AN 8. THERE WAS NO TFC CONFLICT IN XING BILIT 1000 FT HIGH AND THE CAPT DID RPT THE PROB TO MAINT IN DCA. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: FLC HAD ACFT CHANGE AFTER THIS INCIDENT AND WERE NOT ABLE TO FOLLOW UP AT THE TIME. RPTR STATES THAT CAPT CALLED DISPATCH AT END OF DAY TO DETERMINE WHAT MAINT HAD FOUND. APPARENTLY THEY COULD FIND NOTHING ABNORMAL. DISTRESSING TO FLC AS THEY HAD TRIED TO RECREATE THE CONDITION AND ONE WOULD HAVE TO TURN TOO MANY REVOLUTIONS TO NOT BE AWARE OF THE EXTREME SETTING CHANGE. RPTR HAS EXPERIENCED SUCH GLITCHES OF THE LED SWITCHING TO THE NEXT DIGIT INADVERTENTLY BUT NEVER WITH THE ALTIMETER. HE HAS NOT HEARD OF THIS HAPPENING TO ANY OTHER FLC OR ANY OTHER ACFT. THIS ACFT IS EQUIPPED WITH A SYS WHEREBY ONE PUSHES A BUTTON WHEN FL180 ON CLB OR DSCNT TO RESET THE ALTIMETER TO SETTING PLACED IN LOWER AREA. THIS SETTING IS PART OF THE DSCNT CHKLIST AND FLC KNOWS THEY PLACED CORRECT SETTING BECAUSE OTHER ALTIMETER AND STANDBY ALTIMETER HAD THE CORRECT NUMBERS.

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.