An MD88 flight crew required radar vectors to avoid dca airspace.

Attributes
ACN	458463
Time
Date	199912
Day	Thu
Local Time Of Day	1801 To 2400
Place
Locale Reference	navaid : emi.vortac
State Reference	MD
Altitude	msl single value : 20000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zdc.artcc
Operator	common carrier : air carrier
Make Model Name	MD-88
Operating Under FAR Part	Part 121
Navigation In Use	other other vortac
Flight Phase	cruise : level
Route In Use	enroute : direct
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 200 flight time total : 11300 flight time type : 3000
ASRS Report	458463
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : multi engine pilot : commercial
Events
Anomaly	aircraft equipment problem : critical other spatial deviation
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

North of EMI VOR, ZDC said turn 30 degrees right, we were 10 NM off course. Turn accomplished and we reported that our navigation display showed on course. Navigation display did show dead reckoning and no navaids available for ahars positioning. Raw data used for navigation direct to EMI when cleared and latitude/longitude for EMI manually entered into aircraft position. Given a frequency change and next controller told us to proceed direct mol VOR. We turned to this course and after a short time we were again given a heading change because we were encroaching on dca arrival airspace. Once again dead reckoning was displayed on navigation display and raw data was used to navigation to mol VOR when cleared. About 50 NM north of mol VOR, numerous vors appeared on navigation system so ahars unit was able to now locate position accurately. Latitude/longitude position was verified passing over mol VOR. This situation exists in the balance/dca area frequently in glass cockpit aircraft, where dead reckoning annunciates with numerous vors available for positioning. For some reason the automation is confused. With IRU equipped aircraft this is not a big problem, however, ahars aircraft become completely confused. This was the worst case I have experienced, however. Additionally, if you don't continuously monitor raw data, the display indicates that everything is perfect. It is an insidious problem that is difficult to recognize. Ahars performs poorly in this corridor! Callback conversation with reporter revealed the following information: the reporter states that the ahars unit routinely degrades to dead reckoning navigation in the northeast corridor. It is his opinion that the ahars unit is incapable of assimilating data from the numerous sources available. When the unit degrades to dead reckoning, wind corrections are not provided, resulting in off course flight. The degree of displacement depends on the direction and strength of the winds aloft. The navigation displays indicate on course unless raw data selected. Ahars units will normally function in areas outside of the northeast corridor. Degradation to dead reckoning is very seldom experienced, or lasts only momentarily, in these areas.

Original NASA ASRS Text

Title: AN MD88 FLC REQUIRED RADAR VECTORS TO AVOID DCA AIRSPACE.

Narrative: N OF EMI VOR, ZDC SAID TURN 30 DEGS R, WE WERE 10 NM OFF COURSE. TURN ACCOMPLISHED AND WE RPTED THAT OUR NAV DISPLAY SHOWED ON COURSE. NAV DISPLAY DID SHOW DEAD RECKONING AND NO NAVAIDS AVAILABLE FOR AHARS POSITIONING. RAW DATA USED FOR NAV DIRECT TO EMI WHEN CLRED AND LATITUDE/LONGITUDE FOR EMI MANUALLY ENTERED INTO ACFT POS. GIVEN A FREQ CHANGE AND NEXT CTLR TOLD US TO PROCEED DIRECT MOL VOR. WE TURNED TO THIS COURSE AND AFTER A SHORT TIME WE WERE AGAIN GIVEN A HDG CHANGE BECAUSE WE WERE ENCROACHING ON DCA ARR AIRSPACE. ONCE AGAIN DEAD RECKONING WAS DISPLAYED ON NAV DISPLAY AND RAW DATA WAS USED TO NAV TO MOL VOR WHEN CLRED. ABOUT 50 NM N OF MOL VOR, NUMEROUS VORS APPEARED ON NAV SYS SO AHARS UNIT WAS ABLE TO NOW LOCATE POS ACCURATELY. LATITUDE/LONGITUDE POS WAS VERIFIED PASSING OVER MOL VOR. THIS SIT EXISTS IN THE BAL/DCA AREA FREQUENTLY IN GLASS COCKPIT ACFT, WHERE DEAD RECKONING ANNUNCIATES WITH NUMEROUS VORS AVAILABLE FOR POSITIONING. FOR SOME REASON THE AUTOMATION IS CONFUSED. WITH IRU EQUIPPED ACFT THIS IS NOT A BIG PROB, HOWEVER, AHARS ACFT BECOME COMPLETELY CONFUSED. THIS WAS THE WORST CASE I HAVE EXPERIENCED, HOWEVER. ADDITIONALLY, IF YOU DON'T CONTINUOUSLY MONITOR RAW DATA, THE DISPLAY INDICATES THAT EVERYTHING IS PERFECT. IT IS AN INSIDIOUS PROB THAT IS DIFFICULT TO RECOGNIZE. AHARS PERFORMS POORLY IN THIS CORRIDOR! CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATES THAT THE AHARS UNIT ROUTINELY DEGRADES TO DEAD RECKONING NAV IN THE NE CORRIDOR. IT IS HIS OPINION THAT THE AHARS UNIT IS INCAPABLE OF ASSIMILATING DATA FROM THE NUMEROUS SOURCES AVAILABLE. WHEN THE UNIT DEGRADES TO DEAD RECKONING, WIND CORRECTIONS ARE NOT PROVIDED, RESULTING IN OFF COURSE FLT. THE DEG OF DISPLACEMENT DEPENDS ON THE DIRECTION AND STRENGTH OF THE WINDS ALOFT. THE NAV DISPLAYS INDICATE ON COURSE UNLESS RAW DATA SELECTED. AHARS UNITS WILL NORMALLY FUNCTION IN AREAS OUTSIDE OF THE NE CORRIDOR. DEGRADATION TO DEAD RECKONING IS VERY SELDOM EXPERIENCED, OR LASTS ONLY MOMENTARILY, IN THESE AREAS.

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.