The long-delayed NTSB factual report on the Oct. 17, 2000, midair collision over Southern California’s San Fernando Valley not only states objectively what happened but indicates how accidents more often result from a chain of events and circumstances than from a single cause.
On that Tuesday at 3:51 p.m., Gulfstream III N162JC and King Air C90 N1801B briefly occupied the same piece of airspace 2.5 nm north of Van Nuys Airport (VNY) after the Gulfstream had been cleared to land on Runway 16R, and the King Air had been cleared for a straight-in approach to the same runway.
This midair collision, after which both aircraft landed safely without injury to any occupant, missed literally by inches being a disaster in the densely populated neighborhood below. The GIII sustained some quickly repaired damage; the King Air was harmed more substantially.
Controversy immediately swirled around the mishap, as the operators of each aircraft claimed that the other’s airplane overtook theirs from the rear. The Safety Board’s finding of fact, which was originally expected in the summer last year, was published recently.
Who Hit Whom?
The factual report still does not definitively settle the issue of which aircraft overtook the other. The Board’s study of recorded ATC radar data does, however, show that 46 sec before the collision the Gulfstream, owned by actor Jim Carrey (who was not on board) and operated by Trans-Exec Air Service, was approximately 0.2 mi behind, 0.05 mi to the right of and 500 ft higher than the Sun Quest Executive Air Charter twin turboprop. The Board’s finding also revealed several conditions, short- comings and misconceptions that contributed to a merged radar plot. They include:
• An intermittently malfunctioning approach control communication radio transmitter.
• The absence of an air surveillance radar (ASR) repeater display in the Van Nuys tower cab.
• An awkwardly positioned transponder control head in the King Air, which contributed to the lone pilot twice setting a transponder code other than that assigned.
• Van Nuys Tower losing track of the King Air, which controllers had instructed to “make straight-in to Runway 16R” four minutes before the collision.
• A blind spot that may have kept the GIII captain in the left seat (pilot not flying) from seeing the King Air ahead and below after a collision course was established.
Also, eyewitness observations of the collision by people at two separate locations showed that even conscientious, knowledgeable viewers may perceive an event quite differently depending on their relative sight angles. One, a Los Angeles fireman directly under the extended Runway 16R centerline about three miles north of the airport, said he saw the King Air close in on and make contact with the Gulfstream from behind. The other, a flight instructor driving on a freeway about a mile northeast of the first observer, reported seeing essentially what the ATC radar data study revealed.
Taking these factors in order, a reader of the factual report learns that comparing recordings of voice communications made at the Southern California Terminal Radar Control (SoCal Tracon) facility with those made at the transmitter site revealed that “the two transmissions to the Gulfstream at 1549:35 and 1549:50 were among those not transmitted due to SoCal transmitter intermittence.”
Blocked Transmissions
Both those SoCal Approach transmissions (1 min 51 sec and 1 min 37 sec, respectively, before the collision) directed the Gulfstream to contact Van Nuys Tower and advised, “…he’s 12 o’clock a mile, still southbound,” and, 14 sec later, “…altitude unknown, 12 o’clock less than a mile…”
Either of those messages might have alerted the GIII’s pilots to alter pitch angle or heading to unmask the blind spot beneath the Gulfstream’s nose that apparently was hiding the King Air.
At the time of the accident, VNY Tower did not have an ASR repeater, and thus was, for the most part, dependent on radio communication and controllers’ eyes for aircraft under its control. The King Air pilot told the NTSB that after 1547:23, when he was given a discrete transponder code and told to make a straight-in visual approach to Runway 16R, he recalled no advisories from Tower about traffic affecting him. Four minutes 37 sec later (33 seconds after the collision), Van Nuys Tower cleared him to land on Runway 16L.
The ‘Invisible’ King Air
King Air N1801B’s apparent invisibility to Van Nuys Tower resulted in no small part from its transponder being set to 0226 rather than the tower-assigned 0220. The pilot had previously mistaken “6” in the transponder display’s far-right segment for “0” when told by Los Angeles Center to switch from 4626 to 1200 and contact Van Nuys Tower.
Code 0226 was assigned to LAX Tower traffic, and “because the Beech was outside Los Angeles’ airspace, the ATC computer automation software placed the Beech’s radar target display in ‘suspend’ status,” the NTSB report explained. As a result, N1801B’s target was displayed without its altitude and aircraft identification data block, making it impossible for SoCal Approach to pass on accurate information to Van Nuys Tower.
Only when the ATC conflict alert activated 1 min 14 sec before the collision was the Beech’s mode-C altitude and aircraft data displayed. SoCal, which had no previous contact with the King Air, only then was able to identify it. By that time, both N162JC and N1801B were talking on 119.3 MHz, VNY’s Tower frequency.
The NTSB report said the King Air pilot later told an FAA inspector that the Honeywell Bendix/King KT 76 transponder “…installed in a low location and to the right of the center avionics rack…was [in] a difficult location to reach across from the pilot’s seat to set…and read the characters at the same time.”