Probable Cause #13: Circling Into Danger

  • E-Mail this Article
  • View Printable Article
  • Text size:

    • A
    • A
    • A

This article originally appeared in IFR Refresher, March 2005.

Probable Cause

The ceiling was only 300 feet AGL, which was more than 100 feet below the published minimums for the approach. Visibility was marginal at 2-1/2 miles in mist, but it was a dark winter night and the temperature and dew point had already converged at zero degrees Celsius. The news was not all bad; the winds were light, at only six knots from 080 degrees.

The instrument-rated private pilot of a Beech V35B Bonanza was preparing to execute the GPS Runway 35 approach into Chester (KSNC), Conn., and circle to land on Runway 17. Then again, were those really his intentions?

The accident pilot and his passenger were both fatally injured, so we will have to piece together information from the NTSB report, including eyewitness accounts, to gain some insight into the pilot's strategy for the approach.

According to his family, the pilot left his home at approximately 7:00 that morning. He and his passenger flew from KSNC to Roanoke, Va., for a business meeting. After the pilot concluded his business, he called his wife to discuss his return trip. The weather in Connecticut had deteriorated and the pilot told his wife that if he could not complete the approach at Chester, he would divert to the Hartford-Brainard Airport (KHFD), which was close to his house.

At 6:25 p.m., the pilot reported in with New York Approach Control as he was leaving 4,800 feet for 3,000 feet. The controller instructed the pilot to proceed to the Madison VOR and queried the pilot on his choice of approach. Four minutes later, the pilot requested the GPS 35 approach into Chester, with the caveat that he was "not sure we'll get in right now, the automated weather says 300-foot ceiling, but we'd like to try [the] GPS 35." No mention was made of circling to land on Runway 17. More on that later.

The controller instructed the pilot to proceed direct to FLIBB, the initial approach fix (IAF), and passed along the latest weather from nearby New Haven to the pilot. The conditions at New Haven were generally consistent with the Chester weather, although the New Haven ceiling was higher at 700 feet overcast. At 6:44 p.m., the pilot was approaching the IAF and asked for a direct turn into the approach.

The pilot was most likely approaching from the south or west and vectors to final would allow him to avoid the mandatory holding-pattern course reversal at FLIBB. When the pilot was three miles from the FAF, which is the GPS waypoint AKIJE, the controller told him to fly a heading of 010 degrees to intercept the inbound course and to maintain 2,000 feet until established on the approach. He then cleared the pilot for the GPS Runway 35 approach. The pilot repeated the clearance and the controller approved a change to the advisory frequency and instructed the pilot to report canceling IFR in the air or on the ground with flight service.

Radar data was lost 4.5 nm from the airport due to antenna positioning and terrain, but the last track indicated the pilot flew inbound on the GPS Runway 35 approach and had descended to an altitude of 1,500 feet before radar contact was lost. Without radar data or additional ATC communications, we would normally be at a loss to explain what happened next.

Eyewitness Reports

Fortunately, there were two unusually detailed and invaluable eyewitness accounts of the accident. The first witness was outside his home, approximately 1,000 feet northeast of the approach end of Runway 17. He had lived there for 22 years and had observed countless airplanes in the traffic pattern. He had also flown many times with his son, a commercial pilot.

The witness first observed the airplane flying parallel to the runway northbound, 1,000 feet east of the centerline. He estimated the altitude at 400 feet AGL. The position is consistent with a close-in left downwind, circle-to-land approach to Runway 17. The MDA for a Category B airplane is 880 MSL or 464 feet above the airport elevation. The pilot did not have much room for error.

The witness observed the Bonanza make a left turn from the downwind leg to final. With a pattern width of only 1,000 feet, the pilot would not have had room for a normal base leg. The witness was "pretty impressed" that the airplane was able to complete the turn within such a small radius.

To complete the turn in time, the radius of the turn would have had to be a scant 500 feet. To put that in perspective, if the airspeed was 100 knots, a 60-degree angle of bank would have been required. That would equate to a load factor of 2 Gs and a 41-percent increase in the stall speed. Reducing the speed to 90 knots would decrease the required bank angle, but only to about 55 degrees. Stalling the airplane was a real danger. The pilot was in a bad spot and he knew it.

The witness then observed the pilot's final attempt to salvage the ill-fated approach. He commented that he expected to see a much larger angle of bank and that he had never seen an airplane turn "so flat," as he told the NTSB. He added that the airplane seemed slow and that the engine rpm did not increase during the turn.

The results were predictable. As the airplane turned final, it instantaneously changed from wings-level to the left wing pointing straight down and the right wing pointing straight up -- a classic base-to-final spin entry. The witness then lost sight of the airplane but heard it crash.

A flight instructor living one mile north of the field never saw the airplane but heard what sounded like a Bonanza circling to land on Runway 17, as it turned final between the instructor's house and the runway. He confirmed that the airport was "fogged-in" with "low ceilings and visibility." He also estimated the engine RPM at 1,500 to 1,800.

Why Choose To Circle?

The accident pilot attempted one of the most demanding instrument procedures and failed. However, he was not a novice. He had almost 3,000 hours of flight time, 335 hours of night, and 240 hours of actual instrument time. He had completed a BFR and an IPC just three months prior. The NTSB report does not indicate whether the pilot was the owner of the Bonanza, but it appears that he had access to it on a regular basis.

The following morning he had planned to fly with his wife in the Bonanza to visit relatives in Minnesota. The airplane was based at Chester, which implies that the pilot was very familiar with the airport, the surrounding terrain and with the instrument approach procedures. The pilot even had a backup plan and communicated that plan to his wife before departing. So, what went wrong?

The telltale clue is the circling approach. The reported winds were light at only six knots and were exactly 90 degrees off the runway. As a result, there was no advantage in circling to land on Runway 17 versus a straight-in approach to Runway 35. As would be expected, the MDA was slightly higher for the circle-to-land procedure. The pilot already knew the straight-in approach was at or below minimums. Circling would only increase the MDA and substantially escalate the risks. Why would he intentionally plan to circle? It is doubtful that he did.

The runway at the Chester airport is only 2,566 feet long by 50 feet wide and the airport is almost completely surrounded by woods, especially the approach end of Runway 35. The airport has non-standard, medium-intensity runway lights with REIL, but does not have a PAPI or a VASI. The current approach does not depict a VDP, but it would have been located roughly 1.3 nautical miles from the runway. Even a straight-in approach to Runway 35 would have been quite a challenge that night.

The most plausible explanation is that the pilot was in and out of the bases of the clouds and spotted the airport too late to make a straight-in landing to the relatively short runway. Rather than execute a missed approach, the pilot apparently decided to try to salvage the approach by executing a last minute circle-to-land procedure. That might explain why he was so close to the runway on his downwind leg. If this is what actually happened, it was not only unwise, but also illegal.

According to FAR 91.175, in order to operate below the MDA, the aircraft must "continuously be in a position from which a descent to a landing on the intended runway can be made at a normal rate of descent using normal maneuvers." In this case, the key phrase is "intended runway." The pilot is required to immediately execute an appropriate missed approach procedure anytime the above criteria cannot be satisfied after arriving at the MAP. The minimum visibility requirements also apply. Deciding to circle to a different runway after failing to spot the intended runway in time is not permitted under the FARs -- a missed approach is the only legitimate option.

After a long day of business meetings and instrument flying, getting a glimpse of the runway lights at his home airport through the low clouds and mist would have been a powerful enticement to continue the approach. Unfortunately, the pilot gave into temptation and paid the ultimate price, instead of wisely continuing to his alternate.

Manage The Risk

Executing a circle-to-land procedure should not be a last-minute decision. Circling in marginal conditions is legalized scud running and can test even the most experienced IFR pilot to the limit, especially at night. For that reason, many commercial operators prohibit circling approaches. If you decide a circle-to-land procedure is your best option and is worth the additional risk, do your homework in advance.

If a straight-in landing is not an option, you may have a choice to circle-to-land on several different runways. Surface winds, runway lengths, runway widths and terrain will all be important considerations. Keep in mind that crosswind landings are more difficult at night and in marginal visibility due to the lack of visual cues. It is more difficult to determine if you are drifting, which increases the risk of side loads on touchdown. If your landing will be at night, runway and approach lighting configurations will be decisive factors. The availability of a VASI or PAPI will be critically important at night. It is very difficult, if not impossible, to judge your approach angle at night without adequate visual references. A VASI or PAPI will allow you to maintain obstacle clearance on final and complete your approach safely.

Once you have determined the optimal runway, you still have to decide how to get there without hitting anything. Obstacle protection areas for circling approaches are a function of approach speeds, which are based on 130 percent of the aircraft's stall speed in the landing configuration, or 1.3 x Vso. There are five approach categories -- A through E -- each defined by a maximum approach speed. (Category E is reserved for some military airplanes, so most approach plates will only list categories A through D.) Jeppesen lists the maximum approach speeds for each authorized category in the minimums section on every approach chart, a feature that NACO charts doesn't have.

For a given angle of bank, a higher airspeed requires a larger turning radius. The circling approach radii for categories A through E are 1.3, 1.5, 1.7, 2.3, and 4.5 miles, respectively. According to the AIM, "circling approach protected areas are defined by the tangential connection of arcs drawn from each runway end." This is much easier to visualize with the diagram at right: Arcs are drawn with the appropriate radii from the end of each runway. An unbroken line is then drawn from the outside portion of one arc to the next, creating a continuous protected area around the airport.

Each category of aircraft is provided 300 feet of vertical protection from obstacles in the protected areas. Since the radius increases as a function of airspeed, the size of the protected area also increases. The only way to provide the required 300 feet of vertical protection at higher airspeeds is to increase the MDA as additional obstacles intrude in the larger areas. There is no guarantee of any obstacle protection outside of the primary obstacle protection area.

While this is the normal procedure for creating protected areas, there are exceptions. At various airports, circling is prohibited in certain quadrants due to terrain or other sizeable obstructions. Circling may also be prohibited at night. In addition, circling may only be authorized for certain approach categories. For example, only aircraft that meet the category A and B approach criteria are authorized to fly the GPS Runway 35 approach to KSNC. Always review the specific restrictions in the circle-to-land table at the bottom of the approach charts.

After choosing your desired runway and determining which areas are clear of obstacles, there is still work to do. Take the time to review VFR charts to get a better picture of the area immediately surrounding the airport. Examining aerial photographs can also improve your situational awareness and better prepare you for the approach. Pay particular attention to lighted areas that may resemble the runway environment in limited visibility conditions. Look for additional visual landmarks that will help you stay oriented in the pattern.

The Airport/Facility Directory provides the latest information about the airport. Pay particular attention to traffic pattern procedures especially non-standard patterns. The fun is just beginning when you break out of the clouds. In class G airspace, you might find someone else in the pattern. The VFR weather minimums in class G airspace are only one mile visibility and clear of clouds. The same minimums apply at night, provided the airplane is in the traffic pattern and remains within 1/2 mile of the runway. Even if the ceilings and visibility are low, monitor the CTAF frequency and repeatedly announce your position to avoid surprise encounters in the pattern.

Unfortunately, each circle-to-land procedure is different and it is unlikely that they will resemble your typical VFR pattern at 1,000 feet AGL. It is important to plan and practice simulated circling patterns at altitudes ranging from 400 to 800 feet AGL. Practice in visual conditions to learn the optimal pitch, power, flap, and airspeed configurations at each altitude for your airplane. Your standard VFR traffic pattern procedures will no longer apply. Depending on your altitude, you might not need to reduce power until turning final. Practicing circling approaches from various altitudes in VFR conditions will ensure your skills are sharp when you really need them.

Even after entering the pattern with the runway in sight, it is possible to lose sight of the runway at any time, which would require an immediate missed approach. If the conditions are marginal, do not cancel IFR until you are safely on the ground. Keep the missed approach procedure loaded in your GPS and know which direction you need to turn in case you inadvertently fly back into the clouds. It is easy to lose your bearings when you are fixated on maintaining visual contact with the runway environment.

Circling approaches are demanding; they require a unique combination of both IFR and VFR skills. Risk is inherent to these procedures, especially at night. Proficiency and preparation may reduce this risk to an acceptable level, but only you can make that decision.


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