This area of my web site consists of supporting data for my "Petition for Reconsideration." However, it occurred to me that others who do not have a copy of the NTSB report on this midair collision may wish to read it. Therefore I have scanned and included selected portions of NTSB's Report No. NTSB/AAR-85/07 entitled...

Aircraft Accident Report--Midair Collision of Wings West Airlines Beech C-99 (N6399U) and Aesthetec Inc., Rockwell Commander 112TC N112SM, near San Luis Obispo, California, August 24, 1984.

As the basis in my "Petition for Reconsideration" is concerning the very real possibility that the radar data processing methods inherent in the NAS Stage A computer logic may have inadvertently lead to rejection of the Rockwell Commander's target for display to the air traffic controllers, I have selected portions of the report that specifically discuss ATC radar data processing and/or ATC procedures. You will notice that there is no discussion of radar mosaicing, the computer software process of "selective rejection," nor of radar sort boxes...

[Return to Reasonable Doubt Home]

About 1117:38 Pacific daylight time, on August 24, 1984, Wings West Airlines,
Flight 628, a Beech C-99 (N6399U), and Aesthetec Inc., Rockwell Commander 112TC,
N112SM, collided in midair near San Luis Obispo, California, The weather at the time of
the collision was clear. Flight 628 had just departed San Luis Obispo County Airport en
route to San Francisco International Airport, California, and was climbing on a westbound
heading. The Rockwell Commander had departed Paso Robles, California, on a training
flight and was descending toward the San Luis Obispo County Airport on an eastbound
track. The airplanes collided head-on at an altitude of about 3,400 feet. The wreckage of
both airplanes fell into an open field about 8 nmi west northwest of the San Luis Obispo
County Airport. All 17 persons, including the 2 pilots and 13 passengers onboard Flight
628 and the 2 pilots onboard the Rockwell, were killed.

The National Transportation Safety Board determines that the probable cause
of this accident was the failure of the pilots of both aircraft to follow the recommended
communications and traffic advisory practices for uncontrolled airports contained in the
Airman's Information Manual to alert each other to their presence and to enhance the
controller's ability to provide timely traffic advisories.

Underlying the accident were the physiological limitations of human vision and
reaction time. Also underlying the accident was the short time available to the controller
to detect and appraise radar data and to issue a safety advisory.

Contributing to the accident was the Wings West Airlines policy which
required its pilots to tune one radio to the company frequency at all times.

From page 10...

1.17.2 Air Traffic Control Operations

ATC Computer.--A National Airspace Stage A (NAS Stage A) computer is
installed at the Los Angeles ARTCC. The NAS Stage A computer provides radar data and
flight data processing for en route air traffic control. Essentially, raw radar data from
the radar antenna is provided to the Central Computer Complex (CCC), which processes
the radar information and provides the processed data to the Computer Display Channel
(CDC). The CDC, in turn, accepts the data display messages from the CCC and generates
alphanumeric, symbolic, and map data for presentation on the controller's plan view

From page 11...

display (PVD), or radar scope. Data Entry Controls (DEC) at the controllers' operating
positions permit controllers to communicate with the CCC.

The radar data provided by the Los Angeles ARTCC is from its NAS Stage A
en route radar. The NTAP provided the capability to extract track and radar data from
the Systems Analysis Recording (SAR) tape which is recorded after radar data processing
has begun by the CCC and before transmission to the CDC. The NTAP produced listings
for the period between 1100 and 1120 of all 1200 (VFR) and 6721 beacon coded targets in
both system X and Y coordinates and latitude and longitude coordinates in addition to
altitude information. The manager of the FAA's En Route Automation Program testified
that, given the point in the system where the NTAP data is recorded and given the
configuration of the R-15 radar scope at the time of the accident, "There was no
functional reason why [the information displayed on the NTAP data] shouldn't have been
displayed [on the R-1 5 radar scope] ."

The NAS Stage A computer contains a conflict alert program designed to alert
controllers to potentially hazardous traffic situations recognized by the program
parameters that require immediate attention and or action. However, the program will
only function if the airplanes involved are equipped with altitude encoding transponders,
the transponders are operating, and the NAS Stage A computer has identified each
airplane with a given track, i.e., a correlated target. Since the Rockwell Commander's
track had not been inserted into the computer it was an uncorrelated VFR target and the
conflict alert system did not function.

R-15 Radar Sector Controllers

At the time of the accident four controllers were at or near the R-15 radar
position. The R-15 radar controller was a developmental controller 10/ undergoing a
certification check on the R-15 sector, which was being administered by a full
performance level (FPL) 11/controller. The controllers assumed their duties at the
R-15 sector at 1045. The R-15 data position (D position), which is located to the right of
and adjacent to the R-15 radar position, is a nonradar position. The D position was
manned by an FPL controller. A first line supervisor controller was near the R-15 radar
position.

According to the controllers, the radar scope had been set at the 60 nmi range,
and at that setting, 1 inch on the scope equalled 5.45 nmi. With regard to displaying VFR
transponder symbology at the time of the collision, the radar scope had been configured to
display all VFR transponder symbol returns up to an altitude of 24,200 feet. The
testimony of the controllers confirmed that these type of targets were displayed on the
radar scope.

All four controllers said that the traffic at the time of the accident was
"moderate."

R-15 Radar Developmental Controller.--At 1116, when Wings West Flight 628
initially called the Los Angeles ARTCC's R-15 radar sector, the developmental controller
was sequencing two airplanes, Sonic Airlines Flight 766 and United Airlines Flight 1265
for landing at Santa Barbara. (Santa Barbara was portrayed at the bottom right quadrant
of his radar scope.) Because Sonic 766, a slower airplane, was below and ahead of

___________________

10/ A qualified air traffic control specialist who is being trained for a new position or
procedure for career development.
11/ A controller at an ARTCC who is qualified at all sectors in an area of specialization.

From page 12...

United 1265, the controller had to vector United 1265 around Sonic 766 while descending
it below Sonic 766. He said that he "also had to keep an eye on the other airplanes to the
east. I had one aircraft (going) in to Santa Maria (about 20 nmi southeast of San Luis
Obispo) and a couple of other aircraft in there that I had to keep an eye... on."

The developmental controller cleared United 1265 and Sonic 766 from Its
frequency at 1116:23 and 1116:31, respectively, and at 1116:40, he acknowledged
Flight 628's initial call. He testified that the sequencing problem caused a delay because
"There was a lot of coordination to be done with my D controller and the Santa Barbara
approach (control), and when that was all over with, I turned over the two aircraft."
However, he also said that he had to continue to monitor United 1265 "because he was a
little bit high in Santa Barbara. I had to watch to make sure he didn't have to be pointed
out to Sector 14."

The developmental controller also testified that he did not immediately
associate Flight 628's initial radio call with a San Luis Obispo departure and had, in fact,
thought that it was another Wings West airplane, Flight 236, that had called. Therefore,
at 1116:40, he called Flight 236 and told it to 'go ahead)' He scanned his entire radar
scope and saw nothing that he could associate with the radio call. At 1116:46, Flight 628
called "with a request." The developmental controller again told the flight to "go ahead"
and the flight answered" (Unintelligible) intersection, VFR, two point seven climbing, IFR
to San Francisco." He then looked into his "active" traffic strip bay, saw Flight 628's
flight plan, and realized that it was Flight 628 that had called earlier and that it was
departing San Luis Obispo. (The flight plan strip had been placed in the "active" bay by
the D controller.) At 1116:56, he assigned a discrete transponder code to the flight and
tried to locate it on his radar scope. He said he saw a VFR transponder code 12/ just west
of the San Luis Obispo County Airport [top left quadrant of the radar scope and that he
saw this return "right before I saw it turn to a six seven two one code (1117:10)." At
1117:16, he told Flight 628 that he had it "in radar contact," and requested the flight's
altitude. At 1117:20, Flight 628 reported that "it was climbing through 3,100 feet." The
developmental controller testified that there were no other VFR targets on his scope in
the near vicinity of Flight 628 when he reported that he had it in radar contact.

The developmental controller further testified that after he had observed the
discrete transponder code he had looked at Flight 628's flight plan before giving it an IFR
clearance. He said that he had looked around the radar scope while he was reading the
clearance (1117:23) to see where any possible traffic might be. However, since a
northwest bound IFR airplane was at 8,000 feet about 10 nmi south of San Luis Obispo, he
assigned an altitude limitation of 7,000 feet to Flight 628. He said that while there were
"quite a few [VFR targets] down in the Santa Barbara, Santa Maria area," the nearest
VFR traffic he saw was "at least 20 miles" from Flight 628.

At 1117:32, Flight 628 began reading back its clearance. Thereafter, the
developmental controller spoke to two other airplanes. At 1118:40, he tried to contact

_______________

12/ A VFR transponder code would be portrayed on the Los Angeles ARTCC's radar scope
by the symbol "V." If the VFR airplane had an encoding altimeter (Mode C equipment), its
altitude would be displayed next to the "V"; i.e. an altitude of 3,400 feet would be
displayed as "034." When Flight 628 changed to its assigned discrete transponder code,
the VFR symbology would have been replaced initially by a slash and a partial data block
containing the assigned discrete code and the flight's altitude readout until the computer
correlated the assigned discrete code with the airplane's target. Upon completion of the
correlation--two sweeps of the radar antenna--the target symbology would change from a
slash to an asterisk accompanied by a full data block containing the flight's call sign,
altitude, and groundspeed.

From Page 13...

Flight 628 to inform it that the center was no longer receiving its transponder code.
Flight 628 did not answer the radio call and it did not answer any of the subsequent radio
calls.

The developmental controller testified that he had not configured the radar
scope so as to inhibit the display of the VFR transponder symbol. He stated that he did
not see the radar return of the Rockwell Commander, N112SM and that "I know that if it
had been there, I sure would have called it to the Wings West aircraft because it definitely
was traffic from the indications. I cannot understand why it would not have been on my
scope."

FPL Controller at the D Position.--The D controller testified that be was
monitoring the radio transmissions at the time of the collision. He said that he could see
the R-15 radar scope from his position, but that he was not monitoring the screen at that
time because he was involved with administrative and coordination tasks required by the
D position. His duties consisted of making computer inputs, updating flight plans, and
coordinating traffic between sectors. He said that there was no requirement that a
D controller monitor the radar scope.

The D controller also testified that he heard Flight 628's initial call and that
he had then taken Flight 628's flight plan strip from the "proposal" bay, put it in the
"active" bay, and entered a departure message into the ATC computer. At 1116:18, he
received a call on the interphone line from Santa Barbara approach control which required
him to "go and talk to Santa Barbara approach." The ATC transcript showed that this
conversation began at 1116:18 and that the last transmission occurred at 1116:49.

FPL Controller.--The FPL controller administering the certification check to
the developmental controller testified that he was standing directly behind the
developmental controller and was plugged in at the radar so he could, if required, override
the developmental controller's radio transmission to the aircraft under his control. He
had an unobstructed view of the radar scope. He said that he saw Flight 628's radar
return, saw it change from VFR symbology to the correct discrete symbology, and
thereafter, he checked the flight plan strip in the "active" bay to verify that Flight 628's
clearance had been issued correctly. He said that he saw an IFR beacon return about
10 nmi south of San Luis Obispo, however, he did not see any VFR targets to the
northwest of Flight 628. He said that there also were some VFR targets about 20 nmi
away "in the Santa Maria, Santa Barbara area."

The FPL controller stated that he did not observe the Flight 628 target at the
moment it entered coast status. 13/ Since the Los Angeles ARTCC's recorded NTAP
radar data showed that the last transponder beacon signal from Flight 628 was received at
1117:33 the earliest the coast status symbol could have been displayed was 1118:09;
however, the loss of the beacon code was not noticed and reacted to until 1118:40. The
FPL controller testified that he did not notice the loss of Flight 6281 beacon target
earlier because "other parts of the sector had aircraft in [it] and [that] required
attention also. That apparently was the time when [my] attention was [directed back
to] the San Luis Obispo area."

First Line Supervisor Controller. --The Los Angeles ARTCC area supervisor
plugged into the R-15 sector about 1115 to evaluate the developmental controller's
performance.

_______________

13/ When a beacon target is lost or becomes too weak to correlate for three sweeps of
The radar antenna (36 seconds), the track is placed in a coast status. The letters "CST"
are displayed in place of the Mode C derived altitude in the data block.

From Page 14...

The supervisor testified that he had anticipated sequencing problems developing in the
Santa Barbara area and that he wanted to evaluate how the developmental controller
dealt with them. He testified that he was qualified on three other of the center's radar
sectors, but that he was not qualified on the R-15 sector. However, based on his
experience, he was qualified to evaluate the procedures and techniques used by the
developmental controller to control traffic. He said that he could see the R-15 radar
scope but that he did not have any radio override capability.

The supervisor testified that he heard Flight 628's initial call but that he did
not believe that "he was looking at the scope ... I could have been jotting down some
notes, because I did have some comments that I wanted to make to help [the
developmental controller] out on the sequencing situation we had into Santa Barbara at
that time." He said that he did not look at the radar scope while the developmental
controller was talking to Flight 628, and that the first time he noticed the track "it had
already gone into coast-"

From Page 17...

1.17.6 Radar Ground Track Plot and Visibility Studies

The NTAP data showed that both airplanes were recorded as beacon targets
with Mode C altitude information being received by the Los Angeles ARTCC's radar.

The NTAP data for Flight 628 were identified as beacon codes 1200 and 6721
covering a 1 minute 11 second period from 1116:22 to 1117:33. Seven radar returns were
received during this period; the first four were code 1200 returns which were received at
1116:22, 1116:34, 1116:46, and 1116:58; the last three were code 6721 returns which were
received at 1117:10, 1117:21, and 1117:33. The 1117:10 and the 1117:21 returns were
uncorrelated target symbols accompanied by a limited data block; the 1117:33 return was
a correlated target symbol accompanied by a full data block.

From Page 18...

N112SM's radar returns were recorded continuously for 7 minutes 21 seconds
starting at 1110:12 and ending at 1117:33. N112SM's radar returns were identified by
correlating them to the track of Flight 628 and the collision point. In addition, the radar
data showed that N112SM passed abeam Crepe Intersection and was within 10 nmi of the
San Luis Obispo County Airport about 1115:32 and 1117, respectively.

The radar coordinate plot showed that the last returns for each airplane
deviated from their established paths and moved away from each other. The plot was
inconsistent with the physical evidence showing that the airplanes had collided because of
the 'beam splitting" process used by the NAS Stage A radar processing equipment to
resolve the azimuth of two targets in close proximity. Therefore, the tracks of both
airplanes were adjusted to compensate for the deviations produced by the resolution
process. The airplanes' tracks were further adjusted to compensate for transponder
induced range errors. The resultant radar ground track plot produced a collision point
altitude and time of 3,400 feet and 1117:38, respectively. (See appendix E.)

The radar ground track plot indicated that N112SM was either executing or
had executed a slight right turn toward the localizer course at or just before the collision.
However, there was no indication that either pilot performed any type of evasive
maneuver. About 1 minute 16 seconds before colliding (1116:22), the airplanes were
6.8 nmi apart, and, thereafter, they closed on each other on a virtually head-on course at
about 544 fps (322 kn). Given the R-15 radar scope 's distance scale of 1 inch equals
5.45 nmi, the two radar targets would have been about 1.24 inches apart at 1116:22. By
1116:40 and 1117:36, the two radar targets would have closed to about 0.97 inch and
0.4 inch, respectively, on the radar scope.

From Page 22...

2.3 ATC Operations

The Safety Board then sought to determine whether the performance of the
ATC controllers, or the ATC system itself, either caused or contributed to the accident.
The radar ground track plot showed that the accident occurred at 1117:38 and that
Flight 628's radar return (initially as a 1200 code) was not displayed until 1116:22. The
evidence showed that the developmental controller initially communicated with Flight 628
at 1116:40. At 1116:56, he assigned a discrete transponder code to the flight, and, at
1117:16, 22 seconds before the collision, he told Flight 628 that he had it "in radar
contact." Thereafter, he read the flight's IFR clearance to it and listened to the
readback. At 1116:22 the airplanes were about 6.9 nmi apart and the Rockwell was
almost directly in front of Flight 628. Between 1116:22 and the collision, the airplanes
closed on each other at about 544 fps and, except for the Rockwell Commander's slight
right turn, their headings remained the same.

The proximity of the Rockwell Commander to Flight 628 during this period
was such that the developmental controller, had he perceived the developing conflict,
should have issued a traffic or aircraft conflict advisory to Flight 628. In fact, the
developmental controller testified that he would have issued a "safety advisory" if he had
seen the Rockwell Commander's radar return; however, he said that he had not seen the
return, that it had not been portrayed on his scope, and that he did not know the reason it
was not portrayed. Since none of the controllers at the R-15 radar scope testified that
they had seen the Rockwell Commander radar beacon return on his scope, the Safety
Board sought to determine whether it had been displayed, and if it had been displayed,
why it was not seen so that a traffic or aircraft conflict advisory could have been issued
in time to prevent the accident.

The NTAP data reduction showed that processed radar data containing the
Rockwell's and other airplane's VFR transponder symbols were provided from the CCC to

From Page 23...

the CDC. The testimony and evidence showed that, at the time of the accident, VFR
transponder symbol returns were being displayed on the R-15 scope and that the display
controls and display filter key at the R-15 scope were not positioned to inhibit the display
of any VFR 1200 transponder code returns. Since the manager of the FAA En Route
Automation Program had testified that, under these conditions, there was no functional
reason why the Rockwell Commander's radar return, or any other VFR transponder return,
should not have been displayed on the R-15 radar scope, the Safety Board concludes that
the Rockwell radar return had been displayed and that the reason the controllers did not
observe it cannot be attributed to any failure or malfunction of the NAS Stage A's
computers or associated equipment.

The ATC transcript showed that, other then the departure of Flight 628, there
was only one IFR aircraft in the San Luis Obispo area of concern to the developmental
controller. Most of the traffic on the R-15 sector was concentrated in its southern part
and in the Santa Barbara area. At 1116, when Flight 628 initially called, the
developmental controller was in the process of sequencing two aircraft operating in close
proximity to each other for handoff to the Santa Barbara approach control, and he did not
complete the transfer of communications control of the last airplane in the arrival
sequence to Santa Barbara approach control until 1116:31. At 1116:40, the developmental
controller answered Flight 628's initial call. Since the arrival sequence had involved two
IFR air carrier airplanes and coordinating the handoff of these two airplanes to another
ATC facility, the Safety Board believes that the developmental controller's decision to
delay answering Flight 628's initial call until he completed the handoff was a proper
exercise of his discretionary authority. While the developmental controller used an
incorrect call sign in his initial response to Flight 628, this error was corrected almost
immediately and played no part in the accident sequence.

FAA Order 7110.65C requires controllers to "give first priority to separating
aircraft and issuing safety advisories as required in this handbook." However, the
evidence showed that the training provided to the controllers also emphasized that their
primary responsibility is to separate IFR traffic and that the developmental controller had
been "admonished" earlier for providing advisory services to VFR airplanes during
conditions of increased workloads. Since there was only one other IFR airplane near
San Luis Obispo, there was no reason for the developmental controller to direct
continuous attention to that area of his radar scope until Flight 628 called. Although the
developmental controller had handled Flight 628 on its arrival at San Luis Obispo, he did
not know when, or if, it would depart San Luis Obispo, and he was not required to be
aware of this information. Thus, when Flight 628 called to request its IFR clearance, the
developmental controller was faced with the routine tasks of locating the flight,
identifying it, providing it with its clearance, and either separating it from other IFR
traffic, or providing a traffic or aircraft conflict advisory, as appropriate.

The accident circumstances showed that the developmental controller
probably detected Flight 628's VFR transponder symbol just before Flight 628's VFR
symbology changed to an uncorrelated discrete transponder symbol. Flight 628's first
uncorrelated discrete transponder symbol was received at 1117:10, and, at 1117:16,
22 seconds before the collision, the developmental controller told the flight that it was "in
radar contact" and to report its altitude in order to verify the altitude portrayed in the
flight's limited data block. At 1117:23, 3 seconds after the flight reported its altitude and
15 seconds before the collision, the developmental controller issued the flight its IFR
clearance. He said that he looked around his radar scope while he was reading the
clearance and, except for the IFR airplane which prompted him to change Flight 628's
assigned level off altitude to 7,000 feet, he saw no other radar targets near Flight 628.
Flight 628 began its clearance readback at 1117:32, and, at 1117:33, 5 seconds before the
collision, Flight 628's full data block was showing on the radar.

From Page 24...

The facts and circumstances showed that, from the time the developmental
controller began to concentrate on Flight 628, his attention was focused primarily on the
mechanical tasks involved in entering the airplane into the IFR traffic structure. These
tasks included reading from the flight strip, making pencil notations on the strip, scanning
the radar display, and coordinating as necessary with his assistant ("D" side). In addition,
there was evidence indicating that in the little time, if any, the controller took during this
period to scan his radar scope for other traffic, his attention during this search, as a
result of his training, may have been "tunneled" or focused on detecting IFR traffic. The
conclusion that he was aware of IFR traffic is substantiated by his action to change Flight
628's en route altitude, based on an IFR radar return located south of San Luis Obispo (10
nmi behind Flight 628). Nevertheless, he did not observe the Rockwell Commander's VFR
radar return 5 nmi ahead of and closing on Flight 628. In addition, the developmental
controller was concerned that he might have to provide a radar point-out to Sector 14 due
to a potential violation of the sector's airspace by United Flight 1265. This concern might
also have focused his attention away from the area surrounding Flight 628. This focusing
or "tunneling" of mental and visual attention could be one reason the developmental
controller did not detect the Rockwell Commander's radar return, even though it was
displayed on the radar scope within I inch of Flight 628's radar return. The Safety Board
believes that this explanation is far more plausible than the possibility that the
developmental controller disregarded the Rockwell Commander's VFR radar beacon return
because of a priority sequence presented to him in his earlier training.

At 1116:40, when the developmental controller was able to turn his attention
to Flight 628, the airplanes were within 1 minute of colliding. However, in order to
determine which traffic, if any, posed a threat to Flight 628, the developmental controller
had to locate Flight 628 on his radar scope and establish its heading and altitude.
Assuming the developmental controller had sighted the Rockwell Commander at 1117:10,
he would have had about 28 seconds before the collision to evaluate the relative positions
of the two airplanes, perceive the impending collision, and thereafter deliver a timely
airplane conflict advisory to Flight 628 describing the Rockwell's Commander's position
and distance from Flight 628. The time interval within which the developmental
controller's perceptions, decisions, and actions had to be made and performed was
extremely small. In addition, the issuance of a traffic or aircraft conflict advisory at this
point in time would not have assured that the pilots of Flight 628 would either have
detected the Rockwell Commander or, given its dimensions, that they would have
detected it in sufficient time to avoid the collision. However, the Safety Board cannot
rule out the possibility that the issuance of either a traffic or aircraft conflict advisory
would have led to increased efforts by the flightcrew of Flight 628 to detect and avoid a
threatening target. The fact that an advisory was not sent deprived the flightcrew of
Flight 628 of any of the benefits which might have accrued from a higher level of
vigilance, however small they might have been due to the time constraint, and therefore,
the Safety Board concludes it was a contributory factor to the accident. The Safety
Board further concludes that the inability of the controller to detect the conflict and thus
to provide a traffic or aircraft airplane conflict advisory was due to the limited time
available to him to detect and to assess the collision threat, as well as the aforementioned
"tunneling" or focusing of attention.

The R-15 D controller did not see the Rockwell Commander's radar return
because he was not looking at the radar scope at the time of the accident. His primary
duty tasks were administrative in nature and involved coordination tasks connected with
flight plans arrivals, departures, and handoffs to other sectors. There was no requirement
for him to monitor the radar scope presentation, and he was not doing so when the
accident occur.

The FPL controller supervising the developmental controller's certification
check testified that he did not observe any VFR transponder symbol near Flight 628 at

From Page 25...

the time the flight's VFR transponder symbol was changing to a discrete transponder code
symbol. However, his testimony indicated that his attention also was diverted to another
area of the radar scope shortly after the changeover had occurred. After assuring himself
that Flight 628's uncorrelated beacon symbol was being received, and after monitoring the
flight plan strip in the "active" bay to insure that the IFR clearance had been delivered
correctly and receipt acknowledged properly, the FPL controller transferred his attention
to other areas of the radar scope where other traffic was located. He did not observe
Flight 628's radar return again until after the track had entered coast mode. The
evidence indicates that the FPL controller was preoccupied with insuring that the radar
symbology had changed, that the clearance was delivered and received properly, and then,
with monitoring traffic located in another area of the radar scope. Given this narrowing
or "tunneling" of attention, the FPL controller's scan of the radar scope apparently was so
limited that he did not detect the Rockwell Commander's radar return and, therefore he
was unable to detect or point out the presence of the target to the developmental
controller.

The testimony of both the FPL controller and the ARTCC area supervisor
indicated that the major traffic concentration was in the southern portion of the
R-15 sector. The area supervisor said that he had heard Flight 628 call in; however, at
the time of the call he was "jotting down some notes" to critique the developmental
controller's performance during the Santa Barbara sequencing situation, and therefore he
did not look at the radar scope. The evidence indicated that because of his concern with a
higher density traffic area, he was not concerned with the developmental controller's
acceptance of one IFR airplane into an area of low traffic volume. His attention was
concentrated on the completed performance in the Santa Barbara area and he never
observed Flight 628's radar track until after it entered coast mode.

From Page 31... (This is from CONCLUSIONS, 3.1 Findings)

10. Although the R-15 radar sector developmental controller and the FPL
controller said that the radar return of the Rockwell Commander was
not displayed on the radar scope, the evidence indicates that the
Rockwell Commander's radar return was displayed on the radar scope.
The controllers' failure to see it is not attributable to a failure or
malfunction of the NAS Stage A's computers or associated equipment.

11. There was only one other IFR aircraft in the San Luis Obispo area at the
time of the accident, whereas, there was an attention demanding control
situation in the Santa Barbara area located in the southern portion of
the R-15 radar sector. As a result, the developmental controller's
attention was concentrated on the portion of the radar scope which
displayed the southern portion of the R-15 sector.

12. The developmental controller did not establish Flight 628's location on
his radar scope until about 28 seconds before the airplanes collided.

13. With more time available it is likely that the developmental controller
would have detected the conflict and issued a safety advisory.

3.2 Probable Cause

The National Transportation Safety Board determines that the probable cause
of this accident was the failure of the pilots of both aircraft to follow the recommended
communications and traffic advisory practices for uncontrolled airports contained in the
Airman's Information Manual to alert each other to their presence and to enhance the
controller's ability to provide timely traffic advisories.

Underlying the accident were the physiological limitations of human vision and
reaction time. Also underlying the accident was the short time available to the controller
to detect and appraise radar data and to issue a safety advisory.

Contributing to the accident was the Wings West Airlines policy which
required its pilots to tune one radio to the company frequency at all times.

[Return to Reasonable Doubt Home]

The above text was obtained from the NTSB report No. NTSB/AAR-85/07.

This text was scanned for Optical Character Recognition (OCR) processing, followed by manual editing by Tom Lusch for correct presentation on "Lusch's Midair Collision Investigations" web site <http://home.columbus.rr.com/lusch>. Any errors or omissions resulting from scanning process are solely the responsibility of Tom Lusch. Every effort was made to make this an accurate representation of this report.

This page created Mar 18, 2000.

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