Heading track deviation on visual approach.

Attributes
ACN	313814
Time
Date	199508
Day	Sun
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : dtw
State Reference	MI
Altitude	msl bound lower : 3000 msl bound upper : 3000
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : dtw
Operator	common carrier : air carrier
Make Model Name	B757-200
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	descent : approach
Route In Use	approach : visual enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 50 flight time total : 7500 flight time type : 50
ASRS Report	313814
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : less severe non adherence : clearance other anomaly other other spatial deviation
Independent Detector	other flight crewa
Resolutory Action	flight crew : became reoriented flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

Narrative:

Vectors for visual approach to runway 21L changed to runway 21R. Visibility reported greater than 10 mi (ATIS). Actual visibility much lower. Map shift on 757 HSI gave appearance of airport and runway 2 mi further east than actual. Last vector not clearly transmitted by approach control to VFR approach to intercept for visual. While clearing up heading with approach continued on same heading. Aircraft flew into approach corridor for runway 21C. The main safety concern here is an undetectable map shift. When combined with poor visual conditions the tendency is to rely on the map presentation to assist in finding the runway. It would be helpful to have a caution message indicating unreliable map data, especially in the phases of flight where raw data is not readily accessible.

Original NASA ASRS Text

Title: HDG TRACK DEV ON VISUAL APCH.

Narrative: VECTORS FOR VISUAL APCH TO RWY 21L CHANGED TO RWY 21R. VISIBILITY RPTED GREATER THAN 10 MI (ATIS). ACTUAL VISIBILITY MUCH LOWER. MAP SHIFT ON 757 HSI GAVE APPEARANCE OF ARPT AND RWY 2 MI FURTHER E THAN ACTUAL. LAST VECTOR NOT CLRLY XMITTED BY APCH CTL TO VFR APCH TO INTERCEPT FOR VISUAL. WHILE CLRING UP HDG WITH APCH CONTINUED ON SAME HDG. ACFT FLEW INTO APCH CORRIDOR FOR RWY 21C. THE MAIN SAFETY CONCERN HERE IS AN UNDETECTABLE MAP SHIFT. WHEN COMBINED WITH POOR VISUAL CONDITIONS THE TENDENCY IS TO RELY ON THE MAP PRESENTATION TO ASSIST IN FINDING THE RWY. IT WOULD BE HELPFUL TO HAVE A CAUTION MESSAGE INDICATING UNRELIABLE MAP DATA, ESPECIALLY IN THE PHASES OF FLT WHERE RAW DATA IS NOT READILY ACCESSIBLE.

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.