A GPS error placed a BE400 200 ft low and 1/8 of a mile left of bhm runway 36 where a GPWS alerted; ...

Attributes
ACN	1048511
Time
Date	201211
Local Time Of Day	0601-1200
Place
Locale Reference	BHM.Airport
State Reference	AL
Environment
Flight Conditions	IMC
Light	Night
Aircraft 1
Make Model Name	Beechjet 400
Operating Under FAR Part	Part 91
Flight Phase	Final Approach
Flight Plan	IFR
Component
Aircraft Component	GPS & Other Satellite Navigation
Person 1
Function	First Officer Pilot Not Flying
Qualification	Flight Crew Multiengine Flight Crew Instrument Flight Crew Flight Instructor Flight Crew Flight Engineer Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 50 Flight Crew Total 23000 Flight Crew Type 1000
Events
Anomaly	Aircraft Equipment Problem Critical Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Clearance Deviation - Procedural Published Material / Policy Deviation - Track / Heading All Types Inflight Event / Encounter CFTT / CFIT

Narrative:

We had conducted a GPS approach to bhm in accordance with the given wind and prevailing visibility conditions at the time. The approach was conducted in accordance with all directives and procedures. We had expected to break out much earlier; but failing that continued the approach down toward our minimums. At approximately our MDA; I saw what I took to be the overrun markings of the runway. Within seconds I realized that it was not the runway; but a building! At approximately the same time the GPWS warning sounded and we conducted an immediate go-around; both puzzled by the warning; but nonetheless committed to the go-around. Following all procedures we executed the maneuver and subsequently conducted a successful ILS approach to a different runway. As all professional pilots will attest; we later dissected the unusual event that had potential for catastrophe. After all means available to us we concluded that we had followed all parameters for the approach; but for some reason unknown to us the aircraft was not in the position that it thought it was. It was also apparent that the GPS performed correctly and prevented and incident or worse. A contributing factor was that the weather was not at all what had been reported at the time we began the approach; but had deteriorated substantially; with no update by the controller. The reason for this deviation from a safe approach still eludes us.

Original NASA ASRS Text

Title: A GPS error placed a BE400 200 FT low and 1/8 of a mile left of BHM Runway 36 where a GPWS alerted; so a go around was executed followed by a Runway 24 ILS approach.

Narrative: We had conducted a GPS approach to BHM in accordance with the given wind and prevailing visibility conditions at the time. The approach was conducted in accordance with all directives and procedures. We had expected to break out much earlier; but failing that continued the approach down toward our minimums. At approximately our MDA; I saw what I took to be the overrun markings of the runway. Within seconds I realized that it was not the runway; but a building! At approximately the same time the GPWS warning sounded and we conducted an immediate go-around; both puzzled by the warning; but nonetheless committed to the go-around. Following all procedures we executed the maneuver and subsequently conducted a successful ILS approach to a different runway. As all professional pilots will attest; we later dissected the unusual event that had potential for catastrophe. After all means available to us we concluded that we had followed all parameters for the approach; but for some reason unknown to us the aircraft was not in the position that it thought it was. It was also apparent that the GPS performed correctly and prevented and incident or worse. A contributing factor was that the weather was not at all what had been reported at the time we began the approach; but had deteriorated substantially; with no update by the Controller. The reason for this deviation from a safe approach still eludes us.

Data retrieved from NASA's ASRS site as of July 2013 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.

A GPS error placed a BE400 200 ft low and 1/8 of a mile left of bhm runway 36 where a GPWS alerted; so a go around was executed followed by a runway 24 ILS approach.