Map shift on IRS equipped B-757.

Attributes
ACN	286772
Time
Date	199410
Day	Sat
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : buf airport : sdf
State Reference	NY
Altitude	msl bound lower : 35000 msl bound upper : 35000
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zid artcc : zob
Operator	common carrier : air carrier
Make Model Name	B757-200
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	climbout : intermediate altitude cruise other
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : flight engineer pilot : atp
Experience	flight time last 90 days : 100 flight time total : 8000
ASRS Report	286772
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : flight engineer pilot : cfi
Experience	flight time last 90 days : 115 flight time total : 15535 flight time type : 3100
ASRS Report	286775
Events
Anomaly	aircraft equipment problem : critical altitude deviation : excursion from assigned altitude altitude deviation : overshoot non adherence : clearance
Independent Detector	other flight crewa
Resolutory Action	flight crew : overcame equipment problem
Consequence	faa : reviewed incident with flight crew
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

Departed syr for sdf XA28 local. During climb, noticed large map shift on ehsi. Because we normally navigation solely using IRS data, we elected to try to get irss back up to speed. Selected attitude on IRS control panel and, as a result, lost autoplts, autothrottles, flight directors, and had questionable guidance from air data driven instruments. Shortly after this we were given a climbing turn. During the climb, the altimeter indicated a climb and the vsi indicated a descent. We then realized that we were down to the standby instruments. Only problem being the captain's altimeter seems to drive the signal sent by the mode C transponder. We advised ATC of the equipment failures and checked their altitude against ours. They showed us 400 ft high, no traffic conflict. Flight continued uneventfully. We found no guidance for our navigation problem in our quick reference checklist. If we could have read about this system, we would not have selected attitude position on IRS. Supplemental information from acn 286775: due to a self- induced navigation problem our boeing 757 lost all computer generated navigation system and air data computer inputs to the captain's altimeter. The captain's altimeter gives primary information to ATC. At one point in the flight, we were off our assigned altitude 400 ft. We were actually at the correct flight level, but the reporting altimeter was incorrect.

Original NASA ASRS Text

Title: MAP SHIFT ON IRS EQUIPPED B-757.

Narrative: DEPARTED SYR FOR SDF XA28 LCL. DURING CLB, NOTICED LARGE MAP SHIFT ON EHSI. BECAUSE WE NORMALLY NAV SOLELY USING IRS DATA, WE ELECTED TO TRY TO GET IRSS BACK UP TO SPD. SELECTED ATTITUDE ON IRS CTL PANEL AND, AS A RESULT, LOST AUTOPLTS, AUTOTHROTTLES, FLT DIRECTORS, AND HAD QUESTIONABLE GUIDANCE FROM AIR DATA DRIVEN INSTS. SHORTLY AFTER THIS WE WERE GIVEN A CLBING TURN. DURING THE CLB, THE ALTIMETER INDICATED A CLB AND THE VSI INDICATED A DSCNT. WE THEN REALIZED THAT WE WERE DOWN TO THE STANDBY INSTS. ONLY PROB BEING THE CAPT'S ALTIMETER SEEMS TO DRIVE THE SIGNAL SENT BY THE MODE C XPONDER. WE ADVISED ATC OF THE EQUIPMENT FAILURES AND CHKED THEIR ALT AGAINST OURS. THEY SHOWED US 400 FT HIGH, NO TFC CONFLICT. FLT CONTINUED UNEVENTFULLY. WE FOUND NO GUIDANCE FOR OUR NAV PROB IN OUR QUICK REF CHKLIST. IF WE COULD HAVE READ ABOUT THIS SYS, WE WOULD NOT HAVE SELECTED ATTITUDE POS ON IRS. SUPPLEMENTAL INFO FROM ACN 286775: DUE TO A SELF- INDUCED NAV PROB OUR BOEING 757 LOST ALL COMPUTER GENERATED NAV SYS AND AIR DATA COMPUTER INPUTS TO THE CAPT'S ALTIMETER. THE CAPT'S ALTIMETER GIVES PRIMARY INFO TO ATC. AT ONE POINT IN THE FLT, WE WERE OFF OUR ASSIGNED ALT 400 FT. WE WERE ACTUALLY AT THE CORRECT FLT LEVEL, BUT THE RPTING ALTIMETER WAS INCORRECT.

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.