f15: page 3 of 3 - steps 7 to 10

Readings and online activities done by each student individually.

The pilot decided to continue climbing to 8,000 ft altitude enroute to his destination, while keeping an eye on the build-up of ice on the aircraft. He indeed saw some ice accumulate while flying through the clouds at 6,000 ft altitude, but the aircraft was able to continue to climb. He successfully reached the desired enroute altitude of 8,000 ft. So the pilot set the engine throttle to the normal setting for cruise power to maintain the 8,000 ft altitude, to fly to his destination.

Soon the pilot noticed that the aircraft speed wasn't as fast as it should be, and the aircraft started to gradually descend. He contacted air traffic control (ATC) to request a lower flight altitude -- they told him to descend to 6,000 ft altitude. But as he was descending the aircraft quickly accumulated more ice. Since it was still dark outside he could not see the full extent of the ice on the aircraft. His -icing equipment seemed to be working OK, but the aircraft was slowing down, even with full engine power.

About 25 minutes after take-off from Yellowknife, he realized he had problems. He contacted ATC to report severe icing, and he requested a U-turn to return to Yellowknife. The ice was so thick that he could not maintain 6,000 ft altitude, so he requested lower. While descending to the new altitude assignment of 2,100 ft, the aircraft would now and then suddenly tilt nose down briefly, and suddently tilt left or right briefly. The pilot was able to regain control of the aircraft and keep it flying. However, the airspeed was very slow even at full engine power, and the aircraft was still descending.

The aircraft was getting harder and harder to fly, and had another very strong, uncommanded, sudden tilt nose down. "Mayday" the pilot said, the signal that he was declaring an emergency, as he descended below 2,100 ft altitude. More violent uncommanded> nose-down tilts happened while he was only 300 ft above the surface. In the darkness before sunrise, the aircraft made an emergency landing on the frozen ice surface of Great Slave Lake, about 13 km short of the Yellowknife airport.

The aircraft traveled 2,300 feet on the frozen lake surface when it hit an outcrop of rocks that stuck up through the ice. This collision destroyed the nose gear and left main landing gear. The aircraft continued to slide another 600 feet before it stopped.

Everyone survived with no injuries. They were rescued 4 hours later. The aircraft was un-repairable.

crash site photo

Crashed Aircraft

Photos courtesy of the Transportation Safety Board of Canada, further annotated by Stull.

YouTube videos a Cessna Caravan loading, taking off and landing several times in the Canadian bush (You might want to play it at 2x speed).

Source: https://www.youtube.com/watch?v=1CeJ1BAaERY

Extra info for experts; not needed for this course.

Some of the uncontrolled pitch-down movements of the aircraft might have been due to tailplane stall. The design of the tailplane (horizontal stabilizer and elevator) are to produce downward lift at the back of the airplane, to compensate the downward gravitational pull on the engine in the front of the airplane. But with the aircraft loaded too nose heavy, and with ice forming on the tailplane reducing its ability to produce downward lift, the aircraft nose would drop suddenly when the tailplane stalls. See the NASA Glenn Research Center video about tailplane ice.

Source: https://www.youtube.com/watch?v=gSHjs2dhs8A

Post-crash accident investigation	Although the aircraft was not too heavy, the pilot loaded the aircraft incorrectly before take off, so that there was too much weight in the front. As a result, the aircraft was not within the weight-and-balance limits for that aircraft. Normally, the heavy nose could be compensated by the downward force by the tailplane (the tail end of the aircraft) while the aircraft was ice free. However, this didn't work when ice formed on the tailplane. The result was that the nose of the aircraft would, from time to time, suddently tilt down. Namely, the pilot would temporarily lose control of the aircraft. The pilot mis-read the graphical area forecast chart that he got from the internet. (And I presented to you the same mis-interpretion in step 5a - Other Info, so that you would have the same knowledge as the pilot.) Instead of a shallow layer of forecast icing conditions (2,500 to 4,000 ft), the actual forecast icing layer was deep (2,000 to 14,000 ft).
Tips from meteorologists	Icing conditions are very difficult to forecast. As a result, meteorologists tend to be "conservative"; namely, they generally over-predict the threat and intensity of icing. Pilots who use these predictions to decide when not to fly would generally be very safe. But the outcome is many false alarms, in the sense the icing would be forecast when it isn't observed. As a result, some pilots in the Canadian north do not believe the icing forecasts. This is very unfortunate, and for this case study possibly contributed to the unfortunate result.
Tips from flight safety experts	How could this accident have been avoided. Avoid the nose-heavy situation by loading the aircraft properly within the specified weight-and-balance limits. Learn how to read the weather forecast maps correctly, and believe the forecasts. Make a decision to turn around sooner. But it is too easy, and unfair, to judge the outcome after the fact from our armchairs. During an actual flight in difficult instrument conditions when problems start accumulating, the pilot has a very very heavy workload -- all of it stressful. In favour of the pilot for this flight, he continued to try to manage the situation. He never gave up, and as a result was able to land the aircraft and save everyone's lives with NO injuries. Accidents often happen not because of a single problem, but because several problems build on top of each other, until there is nothing the pilot can do to avoid an accident. The trick is to break the chain of compounding mistakes earlier.

If you could start over for this particular case study (knowing the actual outcome from Step 7), what would you do differently as a pilot?

For example, would you make your decision at a different time during the flight planning and the actual flight?

Would you want more or different data to help you make your decision (if so, which data), etc.

Enter your statements into the UBC Canvas system, for the module: Flying f15 - Step 10.

These count towards your grade (for grade weights, see the Evaluation link from the course home page). The grade is based on the relevance of your statements for the scenario of this learning module, and on the indication that you learned from your mistakes (if any), not on the amount of statements you make. Please be brief/succinct.

Image credits. (as stated near the figures)