Air carrier Y aircraft equipment problem autoplt descent through assigned altitude had less than standard separation from air carrier X TCASII RA descend. Evasive action taken.

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Attributes
ACN	267821
Time
Date	199404
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : mol
State Reference	VA
Altitude	msl bound lower : 28000 msl bound upper : 2900
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zdc
Operator	common carrier : air carrier
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	cruise other
Route In Use	enroute : direct
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	climbout : intermediate altitude cruise other descent other
Route In Use	enroute : direct
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 120 flight time total : 4800 flight time type : 1500
ASRS Report	267821
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 113 flight time total : 10700 flight time type : 3155
ASRS Report	267818
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude conflict : airborne less severe non adherence : clearance non adherence : required legal separation other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : overcame equipment problem flight crew : returned to intended course or assigned course flight crew : took evasive action
Consequence	Other
Miss Distance	horizontal : 15000 vertical : 800
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

Air carrier X, over 'mol' VORTAC traveling southwest at .76 mach, FL280 in daylight IMC conditions. X received a TCASII RA alert at cruise in response to an air carrier Y aircraft descending rapidly through FL290. No prior ATC advisory was issued. TCASII commands were manually followed (green arc) after observing RA target at 2 O'clock and 2.5 mi on TA/vsi instrument and verbal 'descend' commands. ZDC advised us of traffic below at 8 O'clock FL270. Descent was halted at FL277 with at TA alert confirming our lower traffic (monitor vertical speed, green arc at zero vvi). Commands were followed as directed by operating procedure and aircraft was leveled off at FL280 after TCASII commands ceased. Air carrier Y stated his aircraft had inadvertently descended through FL290 isolating our IFR separation. Our response was taken because of an immediate and significant hazard brought to our attention by the TCASII system. Observations: workloads permitting, ATC must issue advisories when an aircraft descends rapidly through a cruise or level off altitude especially with 1000 ft separation over a VORTAC or intersection of multiple rtes. Supplemental information from acn 267820: cruise at FL290, automatic pilot on. Aircraft suddenly started climbing. Disengaged and applied forward pressure. Both pitch trim switches had disconnected, re-engaged trim switches and aircraft reversed direction to a descent. Top of climb was 29250 ft, stopped descent at FL288. During descent, received RA to 'monitor vertical speed.' probably caused air carrier X deviations in our vicinity.

Original NASA ASRS Text

Title: ACR Y ACFT EQUIP PROB AUTOPLT DSCNT THROUGH ASSIGNED ALT HAD LTSS FROM ACR X TCASII RA DSND. EVASIVE ACTION TAKEN.

Narrative: ACR X, OVER 'MOL' VORTAC TRAVELING SW AT .76 MACH, FL280 IN DAYLIGHT IMC CONDITIONS. X RECEIVED A TCASII RA ALERT AT CRUISE IN RESPONSE TO AN ACR Y ACFT DSNDING RAPIDLY THROUGH FL290. NO PRIOR ATC ADVISORY WAS ISSUED. TCASII COMMANDS WERE MANUALLY FOLLOWED (GREEN ARC) AFTER OBSERVING RA TARGET AT 2 O'CLOCK AND 2.5 MI ON TA/VSI INST AND VERBAL 'DSND' COMMANDS. ZDC ADVISED US OF TRAFFIC BELOW AT 8 O'CLOCK FL270. DSCNT WAS HALTED AT FL277 WITH AT TA ALERT CONFIRMING OUR LOWER TFC (MONITOR VERT SPD, GREEN ARC AT ZERO VVI). COMMANDS WERE FOLLOWED AS DIRECTED BY OPERATING PROC AND ACFT WAS LEVELED OFF AT FL280 AFTER TCASII COMMANDS CEASED. ACR Y STATED HIS ACFT HAD INADVERTENTLY DSNDED THROUGH FL290 ISOLATING OUR IFR SEPARATION. OUR RESPONSE WAS TAKEN BECAUSE OF AN IMMEDIATE AND SIGNIFICANT HAZARD BROUGHT TO OUR ATTN BY THE TCASII SYS. OBSERVATIONS: WORKLOADS PERMITTING, ATC MUST ISSUE ADVISORIES WHEN AN ACFT DSNDS RAPIDLY THROUGH A CRUISE OR LEVEL OFF ALT ESPECIALLY WITH 1000 FT SEPARATION OVER A VORTAC OR INTXN OF MULTIPLE RTES. SUPPLEMENTAL INFO FROM ACN 267820: CRUISE AT FL290, AUTO PLT ON. ACFT SUDDENLY STARTED CLBING. DISENGAGED AND APPLIED FORWARD PRESSURE. BOTH PITCH TRIM SWITCHES HAD DISCONNECTED, RE-ENGAGED TRIM SWITCHES AND ACFT REVERSED DIRECTION TO A DSCNT. TOP OF CLB WAS 29250 FT, STOPPED DSCNT AT FL288. DURING DSCNT, RECEIVED RA TO 'MONITOR VERT SPD.' PROBABLY CAUSED ACR X DEVS IN OUR VICINITY.

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.