Santa brought smoked bacon (possibly reindeer) with brown sugar. Best Xmas ever! My special Christmas elf and I hope that all of you have a great holiday season with lots of goodies and good times!

I was in a few places in New Hampshire last week, and we ended up spending the night at one of them. Another pilot and I went for a few beers at a Chinese food place right by our hotel, and we spent a couple of hours talking about our dreams and our realities. They gave us fortune cookies at the end of the night, and this was mine:




The other guy's cookie said 'stay away from trees'...

Here's a recent accident report from a medevac flight up north - everyone was okay, but the airplane is a write-off. Too bad, it was the first MU-2 I ever flew and I liked the old girl.


CADORS REPORT

From the report:

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Narrative: The Mitsubishi MU 2B60 aircraft was concluding an IFR flight from Geraldton (Greenstone Regional) Airport (CYGQ) to Armstrong Airport (CYYW). The aircraft landed on runway 30 and encountered an unexpected amount of snow on the runway. The aircraft was unable remain on the runway and came to rest 50 feet south of runway 12/30. There was damage to the landing gear and propeller. There were no reported injuries and all agencies were notified.


UPDATE: a Mitsubishi MU-2 registration C-GAMC was a medevac flight en route from Geraldton to Armstrong Ontario. Earlier in the day the crew checked a NOTAM for Armstrong which indicated that the runway was 100% snow covered, but that snow removal was in progress. Believing that the runway would be clear upon their arrival, the crew conducted a night VFR approach with precision approach path indicator (PAPI) guidance to runway 30. When the aircraft touched down the left main wheel dug into the snow covered surface of runway 30 and veered off to the left eventually departing the runway surface. The aircraft sustained substantial damage to its fuselage, right wing and right propeller. The runway had not been plowed. After the accident, Nav Canada personnel were unable to contact airport operations personnel, and issued a NOTAM to close the airport.

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Man, that sucks. The Armstrong airport is a small airport, north of Thunder Bay, Ontario. It's 4,000 feet long, and covered in ice during the winter. Here's a Google Maps link:


View Larger Map

With smaller airports like this, there aren't a lot of services, and frequently there is nobody around when the airplane lands.

Let's take a closer look at some of the text in the accident report:

"Earlier in the day the crew checked a NOTAM for Armstrong which indicated that the runway was 100% snow covered, but that snow removal was in progress. Believing that the runway would be clear upon their arrival, the crew conducted a night VFR approach with precision approach path indicator (PAPI) guidance to runway 30."

Turns out, snow removal wasn't in progress after all - in fact, the airport personnel had departed the airport and couldn't even be reached after the plane crashed - Nav Canada had to issue a NOTAM closing the airport after the accident.

Anyway, when the crew touched down they landed in a pile of snow and lost control of the plane. That's a hard situation, and I'm left wondering to myself what they could have done differently. I guess they could have done a low approach over the runway to try to ascertain whether or not some of the snow had been removed, but I wonder how much information you can really get while flying over a small airport runway at a few hundred feet at night - even if the runway is plowed, it's gonna be covered in ice, which looks just like snow from above.

I'm sure they called the appropriate unicom frequency before they tried to land, but they wouldn't have expected a reply anyway - it was dark, and at night, and at lots of northern strips there either isn't anyone there, or the airport operator person is sitting in the snowplow out on the runway, and the plow may or may not even have a radio.

It reminds me of a near-accident we had in the MU-2 during a summer flight in 2004 - we were going into a northern gravel strip called Ogoki Post, and we knew from a notam that the runway was being graded and smoothed. No sweat, we flew over the field and saw that the road graders had graded a strip right down the middle of the runway for us. They didn't have radios, but they saw us do a low pass, and they pulled off to the side of the runway for our landing. We had a nice smooth approach, and upon touching down discovered that the road graders had spread a foot of loose gravel over the entire runway, and had plowed the middle section down to maybe about 6 inches of loose gravel. Note: 6 inches of loose gravel absolutely sucks as a landing surface. We nearly lost control of the plane - the nose gear was whipping back and forth in the gravel so hard that the rudder was smacking the stops on both sides like a drumbeat of impending metal-fatigue doom. We got lucky though - the Captain shoved the power levers forward and we had enough remaining speed that we were able to get airborne before we hit any of the trees on the side of the runway. We didn't bother trying again, we just flew home and had maintenance do an inspection of our landing gear and rudder (it was all okay, the MU-2 is built like a tank). It's kinda the same thing as what these poor pilots in the MU-2 encountered in Armstrong a few days ago.

I feel really spoiled now that I fly a jet which isn't allowed to land on gravel strips, and 99.9% of our flights are to large airports that have runway condition reports and snowplows that work 24/7 when it snows.

So here's my question: what would you have done if you were in the position the MU-2 crew was in a few days ago?

I'm at the office as I write these words - taking a break from coding bills and updating some manuals. My plane is down for an engine hot section, which is what I'm gonna babble about today.

Our plane uses Pratt & Whitney JT15D-4 engines, which each produce 2,500 lbs of thrust. This model was the first turbofan engine that Pratt & Whitney ever made, and they got it right the first time.

The overhaul period on these engines is 3,500 hours, with a hot section interval of 1,750 hours. What that means is that after a new (or newly overhauled) engine has accumulated 1,750 hours of air time, they take it apart and check out the bits of it that spin around really fast and heat up - hence the name 'hot section'. After 3,500 hours, they take the whole engine apart and replace most of the moving parts. A typical hot section cost is about $60,000 and a typical overhaul cost is about $350,000. Aircraft ownership is not for the faint of heart :)



First, let's refresh ourselves with basic turbofan operation. This is a cross-section diagram of our engine. The arrows illustrate the airflow, and the colors illustrate the relative temperature.

Basically, air goes through the main (big) fan in the front, and is blown backwards. Some of the air gets ducted along the sides of the engine and never goes through the combustion process, and some of the air goes through another fan near the middle of the engine (called the boost fan because it's not really compressing the air, it's just speeding it up a little) and starts the journey toward the combustion chamber.

If the air goes through the engine, it first gets run through an axial compressor (the dark-shaded spinning disc where the air temperature turns from blue to yellow), then it does a 180 degree turn and goes into the combustion chamber. Fuel is sprayed into the combustion chamber and ignited (the air temperature goes from yellow to red), and the resulting expanded air does another 180, then starts to travel at a great rate of speed toward the back of the engine.

You'll see that the air spins another dark-shaded disk (called the high-pressure turbine because the air is traveling at its fastest when it goes through the turbine), which is directly connected to the same shaft the compressor at the front is - that's how the compressor is powered. Once the air passes through the high pressure turbine, it it blows through another couple of light-shaded disks (the low-pressure turbines, called that because a whole lot of the energy of the air has been depleted by the high-pressure turbine already and the air is moving slower), which are attached to (and power) the main fan and the boost fan at the front. Once it's done all that, the air blows out the back of the engine as straight jet thrust.

It's interesting to note that the air that's ducted along the sides of the engine (and only goes through the big fan at the front) is a much higher volume than the air the goes through the core (and the combustion process). The bypass ratio on our engine is 2.5 to 1, meaning that 2 1/2 times the volume of air goes along the sides of the engine than goes through the core.

It's also interesting to note that the airflow changes direction a couple of times as it goes through the combustion chamber - our engine is called a reverse-flow engine because of that, and it's a design that Pratt & Whitney have favored in many engine models over the years (like their PT-6 turboprop engine which is used in zillions of turboprop aircraft). One of the main advantages of the reverse-flow design is that it reduces the length of the engine; you can see in the drawing that if the red section was a straight line it would be considerably longer. Sure, it makes the engine cross-section wider, but I guess the engineering people have determined that a fatter, shorter engine is better than a long skinny one. Hmm, I'm thinking there's a joke there somewhere, but I'm gonna ignore it and move on...

These are relatively old engines, but they remain popular due to their low fuel consumption and great reliability - on this engine, there are only 6 moving parts (compared to hundreds in your car's engine) and out of the nearly 7,000 JT15D engines built (and more than 40 million flight hours), reliability is well over 99.9%

Okay, that's enough about how the engine works. Now let's talk about the hot section itself, and what they found. Fortunately for me, we got a nice shiny report on the condition of the engine, which I am passing on to you.



Phew, that's a relief. I'd be pretty concerned if the engine wasn't turning freely, or if there were metal shavings in the oil.



No cracks found in the first set of blades, which is welcome news.



The pins that hold the combustion chamber are starting to wear down a bit, but still well within limits.



Moving further inside the engine, still nothing bad to report.



A bunch of fuel nozzle sheaths need to be replaced, and so they shall be. They run about $300 each, but relative to the total cost of the hot section it's pretty minor.



This is definitely good news - the low pressure turbine is fine. Each of those blades is seven hundred bucks, so I'm glad to see they are in good shape.



This single nut needs to be replaced ($550) not because it's in bad shape, but because a newer betterer nut was created after this one was installed, and the maintenance bulletin that talks about this says the old nut has to be switched out during the next scheduled heavy maintenance (hot section or overhaul).



I obviously removed some identifying information, but in summary the engine is behaving how the engine should be behaving. That buys peace of mind, and to me that's well worth the $61.543.22 expense.

So basically that's it - the engine is halfway along the road to a complete overhaul, and it's holding together nice and tight. The overhaul will be in another 1,750 hours, during which they will pull the entire engine apart and replace damn near everything, (at about 6 times the cost of the hot section inspection). Yup, you gotta spend money to run an airplane, but as it's my hind end in the front seat on most of the trips, I am okay with spending it on stuff like this :) One additional note: at the rate we fly, we won't hit 1,750 hours more use for nearly another decade - I won't be trying to achieve that interval between inspections in my Honda Civic any time soon, but that just goes to illustrate how reliable these engines are.