Narrative:

During takeoff from runway 26 at juneau; we heard tower tell a helicopter to remain north of the front course into runway 8. Later we heard the helicopter tell the tower that we were in sight as we made our departure from juneau. During takeoff this aircraft has a high rate of climb; about 3500-4000 FPM. With an accentuated deck angle; combined with the helicopter traffic being predominantly over the ridge line to the north; the flying pilot will never see the traffic under the same circumstances. The captain is the only one allowed to make the takeoffs from juneau while the runway is under construction. Therefore this scenario is likely anytime the weather is VFR and part 121 traffic is departing to the west. During the climbout; we received a 'descend; descend now' command. The closure rate to the traffic at such a high rate of climb results in an unsafe condition. In order to comply with the RA; it is likely that the aircraft would have to go into negative G's in order to alter altitude to remain below the target. I estimate that the helicopter altitude was about 2;500 - 3;000 ft above the airport; when the RA command was issued. The first officer was able to spot the traffic as we went through his altitude; and he estimated him to be about 3/4 of a mile from us at our 2 o'clock position. Therefore; he was likely closer to us as we went abeam.my response was to disconnect the autopilot and autothrottle and immediately reduce the pitch to comply with the RA command. It was clear shortly afterwards that pitch alone was not going to permit a solution. I did bank slightly left; but that maneuver was going to put the target out of view with a bank away. We were in a position of having to trust that the helicopter pilot had us in sight as he had announced; and that he was remaining outside of a hazardous position. The first officer had the helicopter in sight as we went through his altitude at our 2 o'clock position; and I had the target just before he passed abeam of us.technically I do not believe there was any FAA violation from any of us; the helicopter; or ATC. Our clearance was to depart runway 26; climbing to FL200. The helicopter did remain north of the runway 8 localizer course and said he had us in sight. I would question why the helicopter pilot elected to remain so close to the course; especially with the closure climb rate that he had to have witnessed. The first officer has been flying in alaska for longer than me; and he said at one time we had a departure procedure that permitted us to bank left to a heading of 248 degrees after takeoff. That would permit a wider margin for all of us. But it seems that some procedure needs to be established with helicopter flow in juneau; so that separation is adequate enough to prevent an RA command. The event will happen multiple times in these conditions; permitting only the helicopter traffic the ability to see the target climbing up from below them in VFR conditions. With so much helicopter activity in the summer; a repeat event is highly likely. Nothing prevents helicopter traffic from being only 100 ft north of the course to runway 8 and still be in compliance their clearance; and airliner traffic complying with their clearance as they merge flight paths very close together during climb out.

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Original NASA ASRS Text

Title: An aircraft departed JNU Runway 26 after helicopter traffic but at a 3;500-4;000 FPM climb rate was only able to take modified evasive action from the TCAS RA 'DESCEND NOW' command. The First Officer reports the traffic 3;000 ft abeam.

Narrative: During takeoff from Runway 26 at Juneau; we heard Tower tell a helicopter to remain north of the front course into Runway 8. Later we heard the helicopter tell the Tower that we were in sight as we made our departure from Juneau. During takeoff this aircraft has a high rate of climb; about 3500-4000 FPM. With an accentuated deck angle; combined with the helicopter traffic being predominantly over the ridge line to the north; the flying pilot will never see the traffic under the same circumstances. The captain is the only one allowed to make the takeoffs from Juneau while the runway is under construction. Therefore this scenario is likely anytime the weather is VFR and Part 121 traffic is departing to the west. During the climbout; we received a 'Descend; descend now' command. The closure rate to the traffic at such a high rate of climb results in an unsafe condition. In order to comply with the RA; it is likely that the aircraft would have to go into negative G's in order to alter altitude to remain below the target. I estimate that the helicopter altitude was about 2;500 - 3;000 ft above the airport; when the RA command was issued. The First Officer was able to spot the traffic as we went through his altitude; and he estimated him to be about 3/4 of a mile from us at our 2 o'clock position. Therefore; he was likely closer to us as we went abeam.My response was to disconnect the autopilot and autothrottle and immediately reduce the pitch to comply with the RA command. It was clear shortly afterwards that pitch alone was not going to permit a solution. I did bank slightly left; but that maneuver was going to put the target out of view with a bank away. We were in a position of having to trust that the helicopter pilot had us in sight as he had announced; and that he was remaining outside of a hazardous position. The First Officer had the helicopter in sight as we went through his altitude at our 2 o'clock position; and I had the target just before he passed abeam of us.Technically I do not believe there was any FAA violation from any of us; the helicopter; or ATC. Our clearance was to depart Runway 26; climbing to FL200. The helicopter did remain north of the Runway 8 localizer course and said he had us in sight. I would question why the helicopter pilot elected to remain so close to the course; especially with the closure climb rate that he had to have witnessed. The First Officer has been flying in Alaska for longer than me; and he said at one time we had a departure procedure that permitted us to bank left to a heading of 248 degrees after takeoff. That would permit a wider margin for all of us. But it seems that some procedure needs to be established with helicopter flow in Juneau; so that separation is adequate enough to prevent an RA command. The event will happen multiple times in these conditions; permitting only the helicopter traffic the ability to see the target climbing up from below them in VFR conditions. With so much helicopter activity in the summer; a repeat event is highly likely. Nothing prevents helicopter traffic from being only 100 ft north of the course to Runway 8 and still be in compliance their clearance; and airliner traffic complying with their clearance as they merge flight paths very close together during climb out.

Data retrieved from NASA's ASRS site 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.