LAX97FA164

Beech 99 (B99) departed on VFR flight (flt) & began climb to 10,500', heading 175 deg. At boundary of class B airspace, ATC controller (TRACON) terminated radar service as B99 was at 7,000'; 40 sec later, pilots (plts) of Boeing 737 (B737) contacted TRACON, on Cresso 3 Arrival (STAR), & were cleared to descend to 10,000' on converging vector of 020 deg; 50 sec later, TRACON advised B737 of traffic (B99), 3 mi ahead, opposite direction & 1,700' lower. TRACON did not mention traffic was climbing, nor issue safety alert; 18 sec later, TRACON told B737 plts they could 'climb as you wish.' 1st officer (FO, plt flying TCAS equipped B737) responded to a resolution advisory by using autopilot & neglected to press 'level change,' which delayed avoidance maneuver. B737 plts saw B99 at close range; FO maneuvered abruptly to avert collision. B737 flight attendant was injured during maneuver. B99 plt saw B737 behind window post, too late for evasive action. Aircraft passed with estimated 200' vertical & no lateral separation (sepn). TCAS event analysis concluded that if B737 pilots had responded to TCAS advisories, within system design parameters, there would have been 700' vertical sepn without abrupt maneuvering. STAR was in heavily traveled area, often used by plts of small VFR aircraft.

History of flight

On April 18, 1997, at 1824 hours Pacific daylight time, America West Flight 66, a Boeing 737-3S3, N313AW, was maneuvered by the flight crew to avoid a near collision with another aircraft while approximately 25 miles south of McCarran International Airport, Las Vegas, Nevada, during descent for landing on the CRESO THREE arrival route. One flight attendant was seriously injured. The aircraft was not damaged, and the 2 cockpit crew, 2 cabin crew, and 120 passengers were not injured. The scheduled domestic passenger flight was operated under 14 CFR Part 121 by America West Airlines, Inc., and departed Orange County Airport, Santa Ana, California, at 1743 on a nonstop flight to Las Vegas. The flight was operating on an instrument flight rules flight plan and visual meteorological conditions prevailed. The second aircraft was a Beech 99, operated by Ameriflight, Inc., of Burbank, California, under 14 CFR Part 135 and with the call sign Amflight 1898, as a nonscheduled domestic cargo flight from Las Vegas to Ontario, California. Amflight 1898 was operating on a company VFR flight plan.

The location of the accident is approximately 5 miles outside of the Las Vegas Class B airspace southern boundary. The CRESO THREE Standard Terminal Arrival Route (STAR) graphic states that turbojet aircraft on the arrival should expect to cross WHIGG intersection, 43 miles south, at 12,000 feet. The minimum en route altitude from WHIGG intersection to the next fix on the STAR, CRESO intersection, is 10,000 feet.

According to communication transcripts and radar data, Amflight 1898 was a VFR departure outbound from Las Vegas on a southwesterly course (which was approximately the reciprocal of the CRESO THREE arrival course), and was receiving traffic advisories from Las Vegas TRACON while in the Class B airspace. According to the pilot, he had requested radar traffic advisory services for the entire flight to Ontario from McCarran Clearance Delivery prior to takeoff. According to the pilot and the transcript, at the limit of the Class B airspace, the controller terminated radar services at 1826:08. At that point, Amflight 1898 was level at 7,000 feet and then resumed climbing to it's intended en route cruise altitude of 10,500 feet. Forty seconds later (1826:48), the America West flight (call sign "Cactus 66") checked in with the controller on the CRESO THREE arrival near WHIGG intersection at 12,000 feet. Cactus 66 was cleared to descend to 10,000 feet and was issued a [left 13 degree] vector heading of 020 degrees. Fifty seconds later (1827:38), the controller pointed out the traffic to Cactus 66 as "twelve o'clock and three miles opposite direction altitude indicates nine-thousand, three-hundred" then, at 1827:56, told the flight they could "climb as you wish." At 1827:59, Cactus 66 replied "OK, we're gonna have to do that." At 1828:20, the controller told Cactus 66 that traffic was no longer a factor and instructed the flight to descend to 8,000. Cactus 66 acknowledged the descent and added "that was close."

During the course of the investigation, the Safety Board learned that earlier in the same flight Cactus 66 had been involved in a loss of separation (ATC) incident over metropolitan Los Angeles. The incident occurred after departure from Orange County Airport while the flight was under control of the Los Angeles Air Route Traffic Control Center (ARTCC). TCAS was used by the flight crew to avoid a near collision situation without aggressive evasive maneuvering. The fact that another incident had occurred was indirectly alluded to during a review of the cockpit voice recorder (CVR) conversations between the flight crew while on the ground at Las Vegas. At the direction of the Safety Board, the Los Angeles Air Route Traffic Control Center (ARTCC) provided radar data and recorded voice tapes which confirmed the incident. After a review of this data, the decision was made to interview those controllers who were in direct communication with the flight crew at the time of the incident. Those interviews were conducted on May 18, 1997, at Palmdale, California.

Flight Crew Interviews

The America West pilots were interviewed separately on the same day. For the Santa Ana to Las Vegas leg, the Captain was the non-flying pilot and the First Officer (FO) was the flying pilot.

Both pilots said that, as they were descending through about 11,000 feet, a traffic advisory (TA) on the TCAS announced "traffic" either immediately before or after the call from Las Vegas Approach Control advising traffic at 12 o'clock, 3 miles, 9,300 feet. Both pilots said they looked outside in accordance with their training to attempt to acquire the traffic visually. Soon there was a "monitor vertical speed" resolution advisory (RA). Then came the call from approach control authorizing them to "climb as you wish," and the Captain replied "we're gonna have to do that" and gave a "thumbs up" to the First Officer. The First Officer initiated the transition from descent to climbing flight using the autopilot mode control. The Captain recalled no further RA's, however, the First Officer recalled a "climb, climb" RA at the same time they both simultaneously saw the traffic. Both pilots related that they believed a collision had been imminent and that the abrupt pull up was appropriate and necessary. Both stressed the rapidness with which the sequence of events progressed.

The Captain added that prior to WHIGG intersection they had completed the in-range call to the company, made their final cabin announcement, and performed the descent checklist. He recalled that the last time he looked at the TCAS he thinks the traffic was about 300 feet lower. He and FO looked for the traffic, and both saw the other aircraft at the same instant. The captain reached for the controls but didn't use them. The FO handled the evasive maneuver. He doesn't remember the RA, only "traffic - traffic," and he doesn't remember any colors displayed on the VSI. It "all happened together" and "very fast."

Asked if he felt that the First Officer responded correctly and appropriately to the TA and RA, the Captain replied that "I don't see how he could have done anything different given the timeline to respond." According to the Captain, the response was in accordance with their training. When he saw the other aircraft he perceived the collision as imminent and characterized the First Officers flight control inputs as "adequate to miss the other aircraft."

The First Officer's recollection of the sequence of events were similar to the Captain's. In accordance with their training, they looked for traffic but had no contact. He recalled that they received a "monitor vertical speed" RA and ATC gave them the OK to climb if required. He elaborated, however, that when the captain motioned (thumbs up) to climb, he moved the vertical speed control on the autopilot mode control panel to stop the descent and start a climb. The autopilot did not respond because he had neglected to press the "level change button." The Captain saw this and armed level change. There was a "climb-climb" RA about the same time they both saw the other aircraft.

Asked if he had any difficulty interpreting the TCAS display, the First Officer responded that he didn't recall what the TCAS showed at the time. He didn't recall if the traffic was displayed at 4, 5, or 6 miles. The time period from TA to "monitor vertical speed" to RA happened so fast he lost his time perception. He didn't have any comment on difficulty interpreting the TCAS because everything happened so quickly.

Asked if he would do anything different next time the First Officer said that he had replayed the accident in his mind hundreds of times and "wouldn't do anything different." His decision to use the autopilot instead of reverting to manual control through the RA climb is consistent with company policy o