<< >> NASA ASRS Report 457461, December 1999

An MD80 flight crew received a TCASII RA 'descend' from an aircraft turning onto final approach at sea.

Attributes
ACN	457461
Time
Date	199912
Day	Sun
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : sea.airport
State Reference	WA
Altitude	msl single value : 3000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : s46.tracon
Operator	common carrier : air carrier
Make Model Name	MD-80 Series (DC-9-80) Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	descent : approach
Route In Use	approach : visual
Flight Plan	IFR
Aircraft 2
Controlling Facilities	tracon : s46.tracon
Operator	common carrier : air carrier
Make Model Name	Dash 8 Series Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	descent : approach
Route In Use	approach : visual
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 : 20000 flight time type : 10000
ASRS Report	457461
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : multi engine pilot : commercial
Events
Anomaly	conflict : airborne less severe
Independent Detector	other flight crewa other flight crewb
Resolutory Action	none taken : anomaly accepted
Miss Distance	horizontal : 4000 vertical : 400
Supplementary
Problem Areas	Airspace Structure
Primary Problem	Airspace Structure

Narrative:

Was being given vectors to visual approach to runway 16R from east arrival procedure (stadium). At same time, dash 8 was given 'bay visual' from west of airport. Our arrs were nearly coincident over downtown seattle with MD80 just slightly ahead. As we each merged over downtown seattle, our TCASII alarm was activated to 'descend' both aircraft in sight of each other. TCASII instructions overridden. Tower wanted west arrival (the dash 8) to cross over and land on runway 16L and MD80 to cross over and land on runway 16R?! This maneuvering request left room for concern on my part. Tower controller very busy and we had to wait some time for an opportunity to question and verify xover plan. We are asking for trouble here: high volume of radio traffic, close proximity of aircraft to each other, checklist requirements, VFR traffic at bfi on TCASII, frequency change (approach-tower), possible TCASII alarms. Remedy: these approachs must be staggered with matched airspds and no xovers regardless of type aircraft. In addition, this is all being done without regard to passenger perceptions/concerns.

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Original NASA ASRS Text

Title: AN MD80 FLC RECEIVED A TCASII RA 'DSND' FROM AN ACFT TURNING ONTO FINAL APCH AT SEA.

Narrative: WAS BEING GIVEN VECTORS TO VISUAL APCH TO RWY 16R FROM E ARR PROC (STADIUM). AT SAME TIME, DASH 8 WAS GIVEN 'BAY VISUAL' FROM W OF ARPT. OUR ARRS WERE NEARLY COINCIDENT OVER DOWNTOWN SEATTLE WITH MD80 JUST SLIGHTLY AHEAD. AS WE EACH MERGED OVER DOWNTOWN SEATTLE, OUR TCASII ALARM WAS ACTIVATED TO 'DSND' BOTH ACFT IN SIGHT OF EACH OTHER. TCASII INSTRUCTIONS OVERRIDDEN. TWR WANTED W ARR (THE DASH 8) TO CROSS OVER AND LAND ON RWY 16L AND MD80 TO CROSS OVER AND LAND ON RWY 16R?! THIS MANEUVERING REQUEST LEFT ROOM FOR CONCERN ON MY PART. TWR CTLR VERY BUSY AND WE HAD TO WAIT SOME TIME FOR AN OPPORTUNITY TO QUESTION AND VERIFY XOVER PLAN. WE ARE ASKING FOR TROUBLE HERE: HIGH VOLUME OF RADIO TFC, CLOSE PROX OF ACFT TO EACH OTHER, CHKLIST REQUIREMENTS, VFR TFC AT BFI ON TCASII, FREQ CHANGE (APCH-TWR), POSSIBLE TCASII ALARMS. REMEDY: THESE APCHS MUST BE STAGGERED WITH MATCHED AIRSPDS AND NO XOVERS REGARDLESS OF TYPE ACFT. IN ADDITION, THIS IS ALL BEING DONE WITHOUT REGARD TO PAX PERCEPTIONS/CONCERNS.

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.