Probable Cause #30: Extra Attention

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This article originally appeared in Aviation Safety, Feb. 2005.

Probable Cause

The NTSB has several (too many, actually ...) categories it uses to classify aviation incidents and accidents. Among them is the catch-all phrase "improper IFR," which the Board usually uses to describe a pilot executing procedures you won't find in the Aeronautical Information Manual. But there is no similar category for controllers who, for whatever reason, provide substandard and/or confusing service to pilots clearly suffering under a high workload. A good example of how the "improper IFR" label can be applied to controllers as well as pilots -- simultaneously -- occurred on January 23, 2003, when a Cirrus SR20 collided with power lines near San Jose, Calif. The Private pilot/owner was killed in the crash and the airplane was destroyed.

The flight departed the Napa County Airport (APC) in Napa, Calif., with an intended destination of the Reid-Hillview Airport (RHV) in San Jose, Calif. Weather at RHV included a broken cloud layer at 1200 feet, an overcast layer at 8000 feet and visibility of four miles. During the initial portions of the flight after takeoff from Napa, controllers issued numerous radar vectors and altitude assignments to the pilot for traffic avoidance purposes. The NTSB's review of the radar data disclosed that the pilot complied with all instructions.

High Workload

Cirrus SR20

But things began to unravel as the Cirrus was approximately abeam the Oakland International Airport. At this point, a controller instructed the pilot to proceed to navigational fixes near the Palo Alto airport (PAO). The pilot rightly questioned the clearance and the controller subsequently acknowledged his mistaken belief that the pilot was destined to PAO and that the flight was actually destined to RHV. The controller then asked the pilot from which fix he would like to initiate the approach. In response, the pilot requested and received vectors to "around OZNUM," which is the final approach fix (FAF) for the GPS Runway 31R procedure into RHV.

The GPS Runway 31R approach procedure was a fairly new procedure, and was not directly depicted on controllers' display terminals. In order to determine the proper course, controllers had to visualize a line between the airport symbol, and the OZNUM and ECYON waypoint symbols.

After this clearance was given and acknowledged, radar data indicates the airplane turned almost 90 degrees to the right and tracked on a course consistent with proceeding direct to PAO. The controller noticed the course deviation, and queried the pilot. The controller provided no specific headings, but told the pilot to make a right turn to avoid traffic associated with San Jose International Airport, and to proceed to OZNUM. The pilot acknowledged and made a right turn of approximately 270 degrees, briefly tracking on an approximately southbound course, which did not appear to be aligned with any relevant navigational fix. After approximately three miles on that course, the pilot turned left to a heading consistent with proceeding direct to OZNUM, flying overhead RHV, on approximately the reciprocal of the final approach course, i.e., aligned with RHV, and the fixes OZNUM, then ECYON.

Widespread Confusion

Reid-Hillview (RHV) RNAV(GPS) Runway 31R approach chart excerpt. (Click here for larger version -- 200 KB.)

The first controller to handle the flight in the RHV vicinity (L1) later said he became aware of the aircraft when he overheard the previous controller (Saratoga) correct the pilot's course to OZNUM. The L1 controller said he believed the pilot required extra attention and intended to provide what assistance he could. The pilot had no further clearance to follow, since the Saratoga controller had cleared him direct to OZNUM with the expectation that L1 would provide vector service.

At that point, L1's initial instruction was for the pilot to proceed direct to ECYON; the pilot's response was to question the fix. According to L1's statements, he recalled that the airplane was in a position coincident with a downwind leg, and the turn toward ECYON would work out to be the same as a vector to final. Shortly after this exchange, L1 noted the airplane appeared to begin a left turn towards OZNUM, but he instructed the pilot to turn right toward ECYON in order to remain clear of a higher terrain area. At this time, OZNUM was directly behind the airplane, and ECYON at about the four o'clock position. The pilot completed a right turn, briefly flying a course headed to OZNUM, but then made a slight left turn and flew a course consistent with the published segment between ZUXOX and ECYON. L1 said he observed the pilot on this course and issued clearance for the approach.

At this point in its discussion of the accident sequence, the NTSB chose to quote FAA Order 7110.65, the "bible" for controllers, by noting that it specifies that standard approach procedures "shall commence at an Initial Approach Fix or an Intermediate Approach Fix if there is not an Initial Approach Fix. Where adequate radar coverage exists, radar facilities may vector aircraft to the final approach course [by assigning] headings that will permit final approach course interception on a track that does not exceed 30 degrees."

Compounding the apparent confusion in the controlling facility -- and probably fostering it in the cockpit -- a controller change occurred as the flight flew between ECYON and OZNUM. As part of the changeover, L1 advised the second controller (L2) that the aircraft was on the approach and the only remaining task was to issue the frequency change to RHV tower.

During the pilot's initial conversation with the RHV tower, the airplane began a turn to the right approximately over the JOPAN waypoint. The airplane's course had diverged almost 90 degrees from the final approach course.

Shortly after the pilot made initial contact with RHV tower, the Minimum Safe Altitude Warning System (MSAW) alerted. The RHV tower controller cleared the pilot to land then said, "low altitude alert, check your altitude immediately." Based on the radar data, the airplane's projected track was diverging away from the centerline of the approach, and toward higher terrain. At the time of the alert the airplane was at about 1900 feet, and the minimum altitude for the final segment is 1440 feet. About 30 seconds later, the tower controller notified the pilot that he appeared off course. The airplane had clipped power lines and came to rest approximately 032 degrees from the first identified point of contact.

Probable Cause

ATC radar screen

The NTSB determined the accident's probable cause to be the pilot's failure to "maintain the course for the published approach procedure due to his diverted attention. The distraction responsible for the pilot's diverted attention was the ... the confusion surrounding the ATC clearances to get established on the final approach course, which likely involved repeated reprogramming of the navigation system. Factors in the accident include the failure of ATC to provide the pilot with a timely and effective safety alert concerning the deviation from the proper course ..." According to the NTSB, an additional factor was the nonstandard method of providing approach clearance, which likely may have exacerbated pilot task overload.

There's no question that modern cockpits can demand high workloads of solo pilots when a series of missteps by controllers require their time and attention. And, as we have reported in the past, the proliferation of GPS approaches has left many controllers unsure how to handle them at times.

In this instance, both parties -- controllers and the pilot -- should have taken a deep breath and started from scratch by positioning the airplane south of RHV for a straight-in approach. But, pride goeth before a fall, and both ends of the transaction probably believed things were salvageable. Unfortunately, neither gave the flight the extra time and attention it obviously deserved.


More accident analyses are available in AVweb's Probable Cause Index. And for monthly articles about safety, including accident reports like this one, subscribe to AVweb's sister publication, Aviation Safety.