Narrative:

I was flying a police helicopter on the above mentioned date. While on patrol, the helicopter is always in radio contact/control with either WWW or ZZZ towers. At approximately PM40 I was working a call 3 mi ssw of the localizer of runway xxl at WWW. I requested with WWW tower to get closer to the localizer/centerline of runway xxl as inbound traffic would permit. As it turned out the actual call/location was 1 mi ssw of the centerline. I was doing r- hand orbits at 800 ft AGL at 60 KTS. I saw numerous inbound jets pass by me on the visual approach into WWW and acknowledged tower I had those aircraft in sight as they got closer. I proceeded wbound to increase my separation to approximately 2 - 2 1/2 mi and climb in altitude to avoid wake turbulence as the jets passed. As the aircraft cleared, I would return to the area I was working. This one particular incident involved a B737-200 inbound on the runway xxl visual. My orbits were tight so I could see the B737 frequently as it progressed towards the airport. As the B737 approached the landmark (approximately 5 mi out) I completed my last orbit and held an out of ground effect hover (zero ground speed) at 1000 ft above ground level and approximately 2 mi south of the localizer waiting for the B737 to pass. At what I estimate to be a 2 mi lateral separation, the B737 leveled off and announced to tower they were doing a go around based on a TCASII RA. The tower advised the B737 of our location and that we were not a factor. The B737 replied 'it would have been nice if you had told us that before!' further radio xmissions from the B737 indicated that their TCASII was placing us 300 ft and 1/4 mi below. It appears that the TCASII software is either defective or TCASII is not designed to deal with hovering helicopters in close proximity. An observation that our helicopter operation has noticed in the past few yrs, when we are within 2 mi and south of the WWW localizer, many commercial carriers have queried the tower of our location. They state that it appears that we are under them and the RA is to climb. In all instances that I have been involved, I was at same altitude with a minimum of 2 mi lateral separation and always ssw of the aircraft. Possibly TCASII system do not calculate a helicopter's ability to stop in midair and just hover as we do in our operation. Callback conversation with reporter revealed the following information: reporter said the problem with aircraft on approach to WWW airport as pertaining to their receiving TCASII RA's on his helicopter is when he is in the area. He is normally at 500 ft AGL in a clockwise circle in that area. Whenever he receives an advisory from the tower or he notes traffic inbound, he will attempt to hover no closer than 2 mi from the localizer course and stay near 1000 ft MSL, near the altitude of the aircraft on approach, so as to avoid any wingtip vortices or 'downwash' as he called it. He said that arrival aircraft have received TCASII TA's/RA's on his aircraft as far away as 5 mi out on approach, even though he is stationary. There is usually not a problem when the tower advises arrival aircraft of his position and that the rotary will keep visual separation. Reporter said that there is a high turnover in the tower and that training is an ongoing thing all the time. So the problem occurs when the tower is too busy or forgets to advise either the chopper or the inbound aircraft. The reporter will, when the tower forgets, advise the tower that he has inbound traffic and will keep visual on it. It's a catch 22 situation. Everyone knows the problem is there but there is not a real solution in sight. If both parties forget then the inbound air carrier has to respond to their TCASII RA. Reporter can hear on the radio the 'chewing out' of ATC personnel by the flcs. He also noted that the older type of B737's and MD80's appear to have a higher proportion of responses to a false or unneeded TCASII RA. Maybe the solution is for another software change that will allow a hovering helicopter to not create an RA. Even when he is 2 mi off the localizer course, the flight crew will state that he is being shown 'under their aircraft' by their TCASII.

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Original NASA ASRS Text

Title: HELI PLT RPTS THAT ARR ACR ACFT TO RWY XXL PICK UP HIS ACFT ON THEIR TCASII, USUALLY RESPONDING TO THE RA WITH A GAR IF TFC HAS NOT BEEN RPTED TO THEM. THIS OCCURS WHEN HE IS EVEN 2 - 2 PT 5 MI SW OFF THE LOC AND HOVERING AT ABOUT 800 FT AGL.

Narrative: I WAS FLYING A POLICE HELI ON THE ABOVE MENTIONED DATE. WHILE ON PATROL, THE HELI IS ALWAYS IN RADIO CONTACT/CTL WITH EITHER WWW OR ZZZ TWRS. AT APPROX PM40 I WAS WORKING A CALL 3 MI SSW OF THE LOC OF RWY XXL AT WWW. I REQUESTED WITH WWW TWR TO GET CLOSER TO THE LOC/CTRLINE OF RWY XXL AS INBOUND TFC WOULD PERMIT. AS IT TURNED OUT THE ACTUAL CALL/LOCATION WAS 1 MI SSW OF THE CTRLINE. I WAS DOING R- HAND ORBITS AT 800 FT AGL AT 60 KTS. I SAW NUMEROUS INBOUND JETS PASS BY ME ON THE VISUAL APCH INTO WWW AND ACKNOWLEDGED TWR I HAD THOSE ACFT IN SIGHT AS THEY GOT CLOSER. I PROCEEDED WBOUND TO INCREASE MY SEPARATION TO APPROX 2 - 2 1/2 MI AND CLB IN ALT TO AVOID WAKE TURB AS THE JETS PASSED. AS THE ACFT CLRED, I WOULD RETURN TO THE AREA I WAS WORKING. THIS ONE PARTICULAR INCIDENT INVOLVED A B737-200 INBOUND ON THE RWY XXL VISUAL. MY ORBITS WERE TIGHT SO I COULD SEE THE B737 FREQUENTLY AS IT PROGRESSED TOWARDS THE ARPT. AS THE B737 APCHED THE LANDMARK (APPROX 5 MI OUT) I COMPLETED MY LAST ORBIT AND HELD AN OUT OF GND EFFECT HOVER (ZERO GND SPD) AT 1000 FT ABOVE GND LEVEL AND APPROX 2 MI S OF THE LOC WAITING FOR THE B737 TO PASS. AT WHAT I ESTIMATE TO BE A 2 MI LATERAL SEPARATION, THE B737 LEVELED OFF AND ANNOUNCED TO TWR THEY WERE DOING A GAR BASED ON A TCASII RA. THE TWR ADVISED THE B737 OF OUR LOCATION AND THAT WE WERE NOT A FACTOR. THE B737 REPLIED 'IT WOULD HAVE BEEN NICE IF YOU HAD TOLD US THAT BEFORE!' FURTHER RADIO XMISSIONS FROM THE B737 INDICATED THAT THEIR TCASII WAS PLACING US 300 FT AND 1/4 MI BELOW. IT APPEARS THAT THE TCASII SOFTWARE IS EITHER DEFECTIVE OR TCASII IS NOT DESIGNED TO DEAL WITH HOVERING HELIS IN CLOSE PROX. AN OBSERVATION THAT OUR HELI OP HAS NOTICED IN THE PAST FEW YRS, WHEN WE ARE WITHIN 2 MI AND S OF THE WWW LOC, MANY COMMERCIAL CARRIERS HAVE QUERIED THE TWR OF OUR LOCATION. THEY STATE THAT IT APPEARS THAT WE ARE UNDER THEM AND THE RA IS TO CLB. IN ALL INSTANCES THAT I HAVE BEEN INVOLVED, I WAS AT SAME ALT WITH A MINIMUM OF 2 MI LATERAL SEPARATION AND ALWAYS SSW OF THE ACFT. POSSIBLY TCASII SYS DO NOT CALCULATE A HELI'S ABILITY TO STOP IN MIDAIR AND JUST HOVER AS WE DO IN OUR OP. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR SAID THE PROB WITH ACFT ON APCH TO WWW ARPT AS PERTAINING TO THEIR RECEIVING TCASII RA'S ON HIS HELI IS WHEN HE IS IN THE AREA. HE IS NORMALLY AT 500 FT AGL IN A CLOCKWISE CIRCLE IN THAT AREA. WHENEVER HE RECEIVES AN ADVISORY FROM THE TWR OR HE NOTES TFC INBOUND, HE WILL ATTEMPT TO HOVER NO CLOSER THAN 2 MI FROM THE LOC COURSE AND STAY NEAR 1000 FT MSL, NEAR THE ALT OF THE ACFT ON APCH, SO AS TO AVOID ANY WINGTIP VORTICES OR 'DOWNWASH' AS HE CALLED IT. HE SAID THAT ARR ACFT HAVE RECEIVED TCASII TA'S/RA'S ON HIS ACFT AS FAR AWAY AS 5 MI OUT ON APCH, EVEN THOUGH HE IS STATIONARY. THERE IS USUALLY NOT A PROB WHEN THE TWR ADVISES ARR ACFT OF HIS POS AND THAT THE ROTARY WILL KEEP VISUAL SEPARATION. RPTR SAID THAT THERE IS A HIGH TURNOVER IN THE TWR AND THAT TRAINING IS AN ONGOING THING ALL THE TIME. SO THE PROB OCCURS WHEN THE TWR IS TOO BUSY OR FORGETS TO ADVISE EITHER THE CHOPPER OR THE INBOUND ACFT. THE RPTR WILL, WHEN THE TWR FORGETS, ADVISE THE TWR THAT HE HAS INBOUND TFC AND WILL KEEP VISUAL ON IT. IT'S A CATCH 22 SIT. EVERYONE KNOWS THE PROB IS THERE BUT THERE IS NOT A REAL SOLUTION IN SIGHT. IF BOTH PARTIES FORGET THEN THE INBOUND ACR HAS TO RESPOND TO THEIR TCASII RA. RPTR CAN HEAR ON THE RADIO THE 'CHEWING OUT' OF ATC PERSONNEL BY THE FLCS. HE ALSO NOTED THAT THE OLDER TYPE OF B737'S AND MD80'S APPEAR TO HAVE A HIGHER PROPORTION OF RESPONSES TO A FALSE OR UNNEEDED TCASII RA. MAYBE THE SOLUTION IS FOR ANOTHER SOFTWARE CHANGE THAT WILL ALLOW A HOVERING HELI TO NOT CREATE AN RA. EVEN WHEN HE IS 2 MI OFF THE LOC COURSE, THE FLC WILL STATE THAT HE IS BEING SHOWN 'UNDER THEIR ACFT' BY THEIR TCASII.

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.