B737 first officer on visual approach to runway 16C at sea reports TCAS RA on another B737 slightly ...

Narrative:

This report is being submitted to address a specific safety concern. During approach to seattle; ATIS said visual approaches were in use for 16L and 16R. At about 20 miles out we were given vectors to 16C. Another carrier 737; northwest of the field; was also being vectored to 16R at the same time. ATC sequenced the two aircraft on parallel approaches with numerous speed assignments; but the aircraft still ended up almost abeam each other. The other jet was slightly in front of us and above us. ATC gave us a clearance for a visual approach and at 3000 ft MSL we received a 'descend descend' RA on the other carrier. We were assigned a speed (I believe it was 150 KTS). The RA had us descending at 1800 FPM; so I complied per the fom. The RA continued for 1500 ft until about 1800 ft MSL. I then said; 'this is not going to work.' we were well below glide path and approaching 1000 ft AGL with a rapid descent rate and with the 737 in sight; still slightly above and in front of us. The RA was simply going to drive us into the ground. I suspect if we had continued with the RA guidance; eventually we would have received a terrain warning! At 1400 ft AGL I again said to the captain; 'this is not going to work. We need to break off the approach to the left.' he agreed; and as soon as I started to break off to the left and gain some lateral separation; we received a 'clear of conflict' and returned to the visual approach with a stabilized approach at 1000 ft AGL. The remainder of the approach and landing was uneventful. If the TCAS equipment on our aircraft and the other carrier's 737 was all working; the other carrier should have received a climb RA and should have responded. This would have immediately relieved our descend RA. The company should issue an immediate safety alert about this problem. Union safety tells me that this has been an ongoing problem at sea. It should have been resolved the first time it happened. If not issuing an alert; then rewrite the fom to address a descend RA in the descent/landing environment/landing configuration; i.e. How do you execute a go-around with a constant descending RA? Consider turning the TCAS to TA only at 8 miles. Consider asking sea TRACON not to sequence aircraft to 16C with parallel arrivals on 16R.

Original NASA ASRS Text

Title: B737 First Officer on visual approach to Runway 16C at SEA reports TCAS RA on another B737 slightly ahead for Runway 16R. Attempts to comply with the RA are not successful until the reporter turns away from the intruder aircraft.

Narrative: This report is being submitted to address a specific safety concern. During approach to Seattle; ATIS said visual approaches were in use for 16L and 16R. At about 20 miles out we were given vectors to 16C. Another carrier 737; northwest of the field; was also being vectored to 16R at the same time. ATC sequenced the two aircraft on parallel approaches with numerous speed assignments; but the aircraft still ended up almost abeam each other. The other jet was slightly in front of us and above us. ATC gave us a clearance for a visual approach and at 3000 FT MSL we received a 'Descend Descend' RA on the other carrier. We were assigned a speed (I believe it was 150 KTS). The RA had us descending at 1800 FPM; so I complied per the FOM. The RA continued for 1500 FT until about 1800 FT MSL. I then said; 'this is not going to work.' We were well below glide path and approaching 1000 FT AGL with a rapid descent rate and with the 737 in sight; still slightly above and in front of us. The RA was simply going to drive us into the ground. I suspect if we had continued with the RA guidance; eventually we would have received a Terrain Warning! At 1400 FT AGL I again said to the Captain; 'This is not going to work. We need to break off the approach to the left.' He agreed; and as soon as I started to break off to the left and gain some lateral separation; we received a 'Clear of Conflict' and returned to the visual approach with a stabilized approach at 1000 FT AGL. The remainder of the approach and landing was uneventful. If the TCAS equipment on our aircraft and the other carrier's 737 was all working; the other carrier should have received a climb RA and should have responded. This would have immediately relieved our Descend RA. The Company should issue an immediate safety alert about this problem. Union Safety tells me that this has been an ongoing problem at SEA. It should have been resolved the first time it happened. If not issuing an alert; then rewrite the FOM to address a DESCEND RA in the descent/landing environment/landing configuration; i.e. how do you execute a go-around with a constant descending RA? Consider turning the TCAS to TA only at 8 miles. Consider asking SEA TRACON not to sequence aircraft to 16C with parallel arrivals on 16R.

Data retrieved from NASA's ASRS site as of April 2012 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.

Attributes
ACN	871868
Time
Date	201002
Local Time Of Day	1801-2400
Place
Locale Reference	SEA.Airport
State Reference	WA
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Make Model Name	B737-700
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Flight Plan	IFR
Aircraft 2
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Flight Plan	IFR
Component
Aircraft Component	Traffic Collision Avoidance System (TCAS)
Person 1
Function	First Officer Pilot Flying
Experience	Flight Crew Last 90 Days 360 Flight Crew Type 6200
Events
Anomaly	Conflict Airborne Conflict

B737 first officer on visual approach to runway 16C at sea reports TCAS RA on another B737 slightly ahead for runway 16R. Attempts to comply with the RA are not successful until the reporter turns away from the intruder aircraft.