B737 flight crew experiences a TCAS RA with a VFR King air at 7;500 FT after being cleared to climb if visual separation can be maintained.
Synopsis
B737 flight crew experiences a TCAS RA with a VFR King air at 7;500 FT after being cleared to climb if visual separation can be maintained.
Narrative
Climbout on vectored 090 heading; passing approximately 5;800 FT; 250 KIAS with clearance to climb to 13;000 FT MSL. Departure Control issued an amended clearance to 7;000 FT MSL. After the pilot flying changed the MCP to 7;000 FT and the pilot not flying verified; the jet leveled off at 7;000 FT MSL. ATC advised of a VFR King Air approximately ten to twelve miles east; southbound; level at 7;500 FT MSL; and that he had the us in sight. The aircraft was observed; reported by pilot not flying to ATC; and then ATC issued clearance to maintain visual separation and cleared the flight to 13;000 FT. Both pilot flying and pilot not flying verified. MCP was changed to 13;000 FT and the pilot flying started an immediate climb at 250 KIAS. Within five seconds into the climb; with a rate of climb of approximately 2;500 FPM; the crew was alerted via TCAS with 'monitor vertical speed;' immediately followed by 'adjust vertical speed;' then 'descend;' followed by 'maintain vertical speed;' and then 'clear of conflict.' As the aural warnings were being given; the pilot flying was adjusting the flight path of the jet as expeditiously as possible; all the while maintaining visual separation with the sighted aircraft. The pilot flying estimated the distance of the aircraft to be five to seven miles; at the time of the initial aural alert; via both TCAS and eye sight. The end result was that our flight passed above and to the left of the King Air approximately 200 FT vertically and 1/2 mile horizontally. There was no known traffic call made by the King Air to ATC; or ATC to us during all this time. Upon landing and deplaning passengers; the pilot flying debriefed the crew (Flight Attendants and First Officer) and discussed the situation. The A Flight Attendant commented that one passenger had asked during his deplaning if the flight had come close to another aircraft during climbout. No other passenger was known to have commented. The flight continued on uneventfully after the turn. The unexpected climb interruption by ATC might have contributed to 'closing the gap' between subject aircraft in this situation. Leveling off and then given clearance to continue the climb led to the TCAS alerting the crew. When the pilot flying and pilot not flying initially saw the other aircraft; the only aircraft in sight; and TCAS showed the ATC altitude mentioned; the pilot flying felt comfortable that visual separation could be maintained without expecting the resulting alerts and situation. Given the fact that any crew does not know what the TCAS sees; the only result is that the crew accomplish the appropriate reactions as expeditiously as possible. In this case; there were no other aircraft observed visually and; at one point; the pilot not flying observed our aircraft above the TCAS displayed aircraft approximately 300 to 400 FT. It was during this time the pilot not flying recalled hearing the 'monitor vertical speed' followed by 'descend' and was just a bit confused to what he saw on TCAS; heard aurally; and saw visually.
Second reporter narrative
ATC said if we could maintain visual separation; we could climb to 13;000 FT. I feel like the Captain was 'primed to climb'. I may be wrong about the exact timing; but I feel that the Captain began the climb while I was still reading back the clearance. I would've liked to stay at 7;000 FT; but we were climbing before I had a chance to convey that. Events unfolded quickly once the climb began. At about 7;200 FT; we received a TCAS RA of 'monitor vertical speed;' which required a pitch down of approximately five degrees. The Captain began a slow pitch over and we quickly received a 'descend' RA. I don't recall what the target descent was. I believe the Captain was trying to prevent floating our Flight Attendants so I'm not sure if he was reacting to the RA quickly enough. Three to four seconds (I believe) after the 'descend RA'; we received an 'adjust vertical speed' RA; which required a climb of approximately 3;000 FPM. The intruder aircraft was getting fairly close at this point and the Captain was fixated on the aircraft outside the window so while a pitch up was initiated; we never reached the Vertical Speed target. I looked out the window and saw the intruder aircraft bank to the west to avoid us. I estimate the distance of the intruder as it passed our left wingtip to be a half mile and noticed -200 FT on the TCAS; but I can't be sure of the exact vertical separation as the intruder passed us. I believe from the time the Captain initiated the climb to the time the intruder passed us to be around 30 seconds.First and foremost; don't climb while maintaining vertical separation unless you are positive about the situation. The Captain thought the plane was heading southeast (basically paralleling our track); which is why he thought we were okay to climb. I wasn't sure and wanted to say something; but the climb was initiated while I was still on the radio. Better crew coordination could have prevented this by making sure we were both okay climbing visually. In hindsight; I should have gotten off the radio immediately and said to stay at 7;000 but; at the time; I didn't realize how convergent our flight paths were. The other possible prevention lies with ATC. I obviously don't know their requirements but at the time we were told to amend our altitude to 7;000 FT; we were established in a full climb power ascent with a Vertical Speed of at least 2;000 FPM. We both felt that if our climb wasn't interrupted that there would have been no issue. On a much more complex level; the TCAS system itself could be improved. I occasionally fly a Cessna 182 with TAS (Traffic Advisory system). This system isn't as complex as TCAS in that it doesn't issue RA's; but the huge advantage of this system over TCAS is that the intruder aircraft symbol includes a vector line so you know the direction the intruder is flying. I know with the number of targets we see on TCAS; maybe vector lines would clutter the display too much; but if it could be programmed to present a vector on a TA and RA that would greatly help situational awareness during these events.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.