Medium large transport had an intermittent mode C malfunction causing activation of the separation m...

Attributes
ACN	311552
Time
Date	199507
Day	Fri
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : zme
State Reference	TN
Altitude	msl bound lower : 28000 msl bound upper : 28000
Aircraft 1
Controlling Facilities	artcc : zme
Operator	common carrier : air carrier
Make Model Name	Fokker 100
Operating Under FAR Part	Part 121
Navigation In Use	Other
Flight Phase	cruise other
Route In Use	enroute : direct
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	DC-10 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	Other
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	311552
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : atp pilot : instrument
Events
Anomaly	aircraft equipment problem : less severe other anomaly other
Independent Detector	other controllera
Resolutory Action	none taken : anomaly accepted other
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

During cruise at FL280 we were being overtaken by a DC10 at FL270. ATC advised us our mode C showed us 400 ft low momentarily. Our altitude had not changed. The controller advised us that this had activated separation monitoring equipment. Our TCASII showed us at 1000 ft separation throughout the DC10's overtake. Our autoplt was engaged and all altimeters agreed at FL280. ZME was the controling agency at the time.

Original NASA ASRS Text

Title: MLG HAD AN INTERMITTENT MODE C MALFUNCTION CAUSING ACTIVATION OF THE SEPARATION MONITORING EQUIP.

Narrative: DURING CRUISE AT FL280 WE WERE BEING OVERTAKEN BY A DC10 AT FL270. ATC ADVISED US OUR MODE C SHOWED US 400 FT LOW MOMENTARILY. OUR ALT HAD NOT CHANGED. THE CTLR ADVISED US THAT THIS HAD ACTIVATED SEPARATION MONITORING EQUIP. OUR TCASII SHOWED US AT 1000 FT SEPARATION THROUGHOUT THE DC10'S OVERTAKE. OUR AUTOPLT WAS ENGAGED AND ALL ALTIMETERS AGREED AT FL280. ZME WAS THE CTLING AGENCY AT THE TIME.

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.

Medium large transport had an intermittent mode C malfunction causing activation of the separation monitoring equipment.