<< >> NASA ASRS Report 339337, June 1996

An air carrier DC10-40 departed dtw with only two of its three INS operative. En route there was a divergence between the two INS. ARTCC was notified. Overwater operation. Foreign airspace.

Attributes
ACN	339337
Time
Date	199606
Day	Sat
Local Time Of Day	0001 To 0600
Place
Locale Reference	atc facility : lnd
State Reference	FO
Altitude	msl bound lower : 35000 msl bound upper : 35000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : eggx
Operator	common carrier : air carrier
Make Model Name	DC-10 40
Operating Under FAR Part	Part 121
Navigation In Use	Other
Flight Phase	cruise other
Route In Use	enroute : atlantic
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 : 23000 flight time type : 750
ASRS Report	339337
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 180 flight time total : 10000 flight time type : 180
ASRS Report	339340
Events
Anomaly	aircraft equipment problem : less severe other anomaly other other spatial deviation
Independent Detector	aircraft equipment other aircraft equipment : unspecified other controllera other flight crewa
Resolutory Action	controller : issued new clearance none taken : unable
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

We were dispatched with only 2 inertial navigation system (INS). Normally it is not a problem, but this time the 2 system were as much as 16 mi apart. We advised shanwick while on high frequency we had degraded navigation. When we checked in at 50N and 15W, radar idented us 9 NM south of track. Supplemental information from acn 339328: a coast out check over maine was good. By the mid-atlantic, the 2 INS were drifting apart, showing an approximately difference of about 10 NM east to west and about 9 NM north to south. We were paralleling other traffic 2000 ft lower about 6 NM to our north the entire crossing. Just west of 15W we passed to shanwick that our navigation was off by as much as 10 NM. Upon receiving jersey, we intercepted the appropriate course and performed a successful position update. The 2 units showed about 16 NM apart. On shutdown, both units met all INS accuracy.

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Original NASA ASRS Text

Title: AN ACR DC10-40 DEPARTED DTW WITH ONLY TWO OF ITS THREE INS OPERATIVE. ENRTE THERE WAS A DIVERGENCE BTWN THE TWO INS. ARTCC WAS NOTIFIED. OVERWATER OP. FOREIGN AIRSPACE.

Narrative: WE WERE DISPATCHED WITH ONLY 2 INERTIAL NAV SYS (INS). NORMALLY IT IS NOT A PROB, BUT THIS TIME THE 2 SYS WERE AS MUCH AS 16 MI APART. WE ADVISED SHANWICK WHILE ON HIGH FREQ WE HAD DEGRADED NAV. WHEN WE CHKED IN AT 50N AND 15W, RADAR IDENTED US 9 NM S OF TRACK. SUPPLEMENTAL INFO FROM ACN 339328: A COAST OUT CHK OVER MAINE WAS GOOD. BY THE MID-ATLANTIC, THE 2 INS WERE DRIFTING APART, SHOWING AN APPROX DIFFERENCE OF ABOUT 10 NM E TO W AND ABOUT 9 NM N TO S. WE WERE PARALLELING OTHER TFC 2000 FT LOWER ABOUT 6 NM TO OUR N THE ENTIRE XING. JUST W OF 15W WE PASSED TO SHANWICK THAT OUR NAV WAS OFF BY AS MUCH AS 10 NM. UPON RECEIVING JERSEY, WE INTERCEPTED THE APPROPRIATE COURSE AND PERFORMED A SUCCESSFUL POS UPDATE. THE 2 UNITS SHOWED ABOUT 16 NM APART. ON SHUTDOWN, BOTH UNITS MET ALL INS ACCURACY.

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.