Sunday, May 03, 2009

Broken Circle

On January 3, 2009 at 1710 mountain standard time (MST) a Learjet 45, N279AJ, sustained substantial damage when attempting to land during a snowstorm at Telluride Regional Airport (KTEX), Telluride, CO. The airplane was owned by LJ279, LLC, Missoula, MT and operated by Aero Jet Services, Scottsdale, AZ. The CFR 49 Part 91 positioning flight was conducted using instrument flight rules and had departed Scottsdale Airport (KSDL), Scottsdale, AZ at 1503 MST. The pilot occupying the left seat was not injured and the pilot occupying the right seat received minor injuries. Both pilots were able to exit the airplane unassisted.

The circle-to-land maneuver is one of the more risky activities that you may do under instrument flight rules, second only to the contact approach. Many freight operators manage these risks by prohibiting their pilots from executing circle-to-land maneuvers at night and most part 121 operators prohibit circling approaches altogether. To understand why a circling approach is potentially more dangerous than a straight-in approach, you need to understand why these minima exist and the challenges that pilots face when executing the circle-to-land maneuver.

Examine the Circular File
One of several situations that require a circle-to-land maneuver is when an approach procedure's final approach course is more than 30˚ out of alignment with any runway at the airport (15˚ for GPS approaches). In these cases, no straight-in approach minima will be published, the approach name will use a letter (starting from the beginning of the alphabet) instead of a specific runway, and the pilot must adhere to the circling minima. This approach into Hanford, California has a final approach segment that is at a right angle to both runways, so you may have no choice but to enter a modified traffic pattern and circle to land on either runway 32 or 14. If you acquire the necessary visual references early enough, nothing in the regulations prevents you from maneuvering early for a straight-in landing.

The NDB or GPS-A approach to Lakeport terminates at the NDB (which has been out of service for almost as long as I can remember) and the pilot must fly visually to the airport, provided they have the necessary visibility and high enough cloud ceiling. It is important to realize that if you begin flying a visual segment like this, then lose visual references and decide to execute the missed approach, it's likely you won't have the normal 40:1 obstruction clearance that you would if you began the missed approach at the missed approach point. Anytime you elect to fly the missed approach, you best climb like a striped monkey (i.e. at your aircraft's best rate of climb) until you reach a safe altitude.

Many pilots don't know or never learned that circling minima will also be provided when the descent gradient from the final approach fix to the runway threshold exceeds 400 feet per nautical mile, even when the final approach course is aligned with the runway. The reason is simple: You may arrive at the missed approach point, visually acquire the runway, yet be too hight to execute a landing using normal maneuvers. This is exactly what happened to the accident flight crew.

One of my favorite examples is the Gillespie LOC-D approach. The localizer is aligned with the runway, but no straight-in minima are published due to terrain and obstructions.

Finally, circling minima are often published in addition to straight-in minima. The circling minima, which are usually higher, allow the pilot to descend on the approach and, once they have the necessary visual references and are at or above the circling minima, maneuver to land on a different runway. This can be advantageous if the surface winds are favoring a different runway for which there is no instrument approach.

The Telluride LOC/DME RWY 9 approach has both straight-in and circling minima, but unlike most approaches, the straight-in minima and the circling minima are the same. I don't know if this is the approach that the accident flight crew was flying, but it likely was because the localizer offers the lowest minima of any of the approaches into that airport.

Manage the Risks
NACO instrument approach charts provide an inset map that shows the airport runway layout, relevant obstructions, and the final approach course relative to the runways. If you are using Jepp charts, you'll need to have the airport diagram out and at the ready, but that diagram won't show the approach course relative to the runways.

On reason the circle-to-land maneuver is more risky is that the pilot must transition from flying on instruments to flying by visual references and then begin maneuvering in a modified traffic pattern fashion. Throw in poor visibility, high surface winds, or night conditions and you've got yourself a real handful. Often the circling MDA is lower than the normal VFR traffic pattern and the obstruction clearance while circling in the protected area is a mere 300 feet, which means it can be really easy to run into something. The size of protected area for circling depends on the aircraft's approach speed, and generally speaking, the larger the aircraft, the faster the approach speed.
  • Category A is for aircraft flying at 90 knots or less
  • B: 91 - 120 knots
  • C: 121 to-140 knots
  • D: 141 - 166 knots
  • E: 167 knots and above

The diagram shows an idealized runway environment. Many instrument approaches contain a notice that the circling is not allowed in certain areas around the airport, due to obstructions. And some approaches specify that circling is not authorized at night. The Telluride approach is a good example of both. But of greater interest is that the approach speed of a Lear 45 may have required category C minima, which are not authorized on this approach.

In a statement provided by the Pilot-In-Command (PIC), upon arrival to KTEX the weather was reported to be below minimums; the crew elected to hold over the Cones VOR and wait to see if weather conditions would improve. The crew was given instructions, by air traffic control, to hold as published and to expect further clearance (EFC) at 1630. When the weather improved to a visibility of 4 miles and a ceiling of 2300 feet, the PIC requested a descent and approach to KTEX. At approximately 4 miles from the airport, the pilot acquired the airport environment but was not in position to land, so he called for a missed approach back to Cones VOR.

If your destination airport is reporting conditions below minima, you are not prohibited under part 91 from attempting the approach. The accident aircraft was reportedly being repositioned under part 91, but the crew elected to adhere to part 135 and 121 requirements of not beginning the approach unless landing minima were being reported at the surface. They even waited until the weather improved to considerably better than the circling minima and they had a plan B, too. But things went South from there.

The pilot then requested a second attempt to land stating that "if we did not land, we would like to be sequenced to into KMTJ" Montrose Regional Airport Montrose, CO, their alternate airport. On the second approach, both crew members stated that they had acquired the runway environment; however, they were still too high for a visual approach. The crew elected to do a 360-degree, right, descending turn, in order to get in a better position for landing. On completion of the turn, they again affirmed the runway environment and that they were aligned with the extended centerline of the runway. The airplane touched down and after full thrust reversers were deployed, the nose gear collapsed. The airplane began to slide in snow and came to a stop about mid-field, in an upright position.

Let the Circle Be Unbroken
The preliminary accident reports stated that the accident aircraft actually failed to touch down on the runway, which is curious given that the localizer appears fairly well aligned with the runway centerline. Did the crew become distracted or disoriented by the poor visibility and blowing snow?

An on-scene investigation was conducted by a Federal Aviation Administration (FAA) inspector. The initial examination of the area indicated that the airplane had touched down about 20-feet to the right, of the runway. Additionally, the airplane's wings were torn from the fuselage and the tail section had separated just aft of the engines, during the contact with the ground.
Weather reported at KTEX 10 minutes prior to the accident was winds 260 degrees at 8 knots, visibility of 3 miles, scattered clouds at 400 feet, broken clouds at 2300 feet, temperature of 6 degrees Celsius, dew point of 6 degrees Celsius, and altimeter setting 29.85 inches of mercury.

Should you need to fly a circling approach, turn up the sensitivity on your spidey senses and consider some techniques that may prevent you from becoming an accident statistic.

If the surface winds are not aligned with the straight-in runway, you probably have a tailwind on the approach. Monitor your groundspeed carefully and consider configuring gear and flaps as necessary to control your groundspeed. Be prepared for a faster than normal speed when you break out and acquire visual references.

Slowing down will also aid you in the circling maneuver since a slower speed will give you a higher rate of turn and a smaller radius of turn with a shallower bank angle.

If the surface winds are high and you'll need to circle, you may want to go to your alternate. Even if the ceiling and visibility are above circling minima, high winds may just ruin your day.

Should you lose visual references while circling, don't kid yourself; it's time to get out of Dodge. Begin climbing, remaining in the protected circling area if necessary, and execute the missed approach ASAP.

Use the VASI and PAPI. If you stay on or above the glide path and within 10˚ of the centerline, you'll be guaranteed obstruction clearance within 4 miles of the threshold.

If ATC gives you advance notice of a need to circle, it will sound something like this:

Barnburner 123 is two miles from Mooselips, fly heading 230, maintain 3000 until established, cleared for the ILS 25, circle runway 7.

When landing at a towered airport, expect the controller to give you a cardinal direction to turn, such as:

Barnburner 123, at minimums, circle south, enter left traffic, runway 9.

Here is an illustration of various ways that a circling maneuver might be conducted, but keep in mind any circling restrictions at your particular destination.

If you have to fly the missed approach once, you may well be better off going to your alternate rather than risking a second approach. The risks of attempting multiple approaches to the same airport are subtle, but very real.

Circle-to-land maneuvers must be demonstrated on an instrument rating practical test and on an instrument proficiency check, so instrument-rated GA pilots should be familiar and proficient with the maneuver. But if the need arises for you to circle-to-land on a real-world instrument approach, be aware that you're doing something that entails more risk than a straight-in approach and landing. Like the accident flight crew, you may be better off executing Plan B and going to your alternate.


david said...

I've always thought of circle-to-land as more dangerous than a contact approach (at least a straight-in one), but I've never checked the stats. Personally, I've flown both, but only with ceiling and vis well above minima.

Ron said...

The Santa Monica (KSMO) VOR-A approach is another one which is perfectly aligned with the runway, yet has no straight-in minimums.

That approach has several challenges, even though it looks simple on the surface. Check out the missed approach point -- it's on the departure end of the runway.


Aviate You said...

Unfortunately, the Lear 45 & Crew is not authorized for this approach. They were negligent and reckless in their attempt to land at Telluride as it is certified for Category A & B aircraft only. I have over 4000 hours in the Lear Series and have operated in and out of Telluride for the last 7 years. If you respect the limitations of the airport. You will be fine.