Dave Fry, WVFC CFI and Aviation Safety Counselor firstname.lastname@example.org
Of Atmospheric Impellers and Pasta
(The Spaghetti’s in the Fan Again)
Mostly, we don’t think of things like autopilots as essential equipment, nor do we consider an autopilot failure as an emergency. Like everything else in the world of aviation, a lot depends on context. Murphy, for example, asserts not only that if anything that CAN go wrong will do so, it will go wrong at the worst possible time. And therein lies our story.
Departing Hayward in a Pilatus on a charter flight to Napa, then on to Redding (there to spend the night – Oh, joy!) and return, our intrepid pilot and unwitting passengers are climbing through 400 feet, starting the crosswind turn, and getting the call from Hayward Tower, “Contact Oakland Tower”. At this point, the brakes have been tagged lightly, the gear is already up, and the Yaw Damper button has been pressed, and everything is under control. Actually, it isn’t – Murphy has already arrived, and the pilot notices the lack of a YD display on what I call the Command Line of the Attitude Indicator – meaning that the Yaw Damper button push didn’t actually turn it on. Simple fix, push it again, press the frequency flip-flop button on the number 1 comm, and listen to get a word in edgewise on Oakland Tower.
At this point, the pilot notices that not only does the YD not appear, Murphy has provided a pair of bonuses – scorched insulation smell, and a red PTRM notice on the Command Line as well as a red TRIM light on the Autopilot. Not Good. Red lights in cockpits pretty much mean something bad.
At the same time, the cotton-picking, finger-licking, chicken-plucking Autopilot voice (Bitching Bertie) at two second intervals starts yelling, “Autopilot, Trim.” Meanwhile, the Pilatus is climbing toward Charlie and Bravo airspaces at around 2,000 FPM with no autopilot to cause a level off, and heading forward toward Charlie at about 150 Kts, so there isn’t a lot of time in which to do SOMETHING. And, oh by the way, our pilot better get the flaps up before busting the max flap speed of 163. Pushing the nose down, pulling the power a lot, and snagging the flap lever into the UP position, the pilot manages to make a call to Oakland Tower, but Bertie is still screaming “Autopilot, Trim”, overriding 75% of what Oakland had to say– and of course, there’s no volume control on Bertie. The pilot does hear something about following 580, but in his rattled mental state, doesn’t consider that 580 actually goes two directions, so he hangs a right to head away from all the problems and starts flying toward Stockton rather than toward Oakland. Oakland Tower, of course is as confused at this point as our pilot, and politely asks our pilot what he’s doing. Only half of which the pilot hears since Bertie simply won’t bloody shut up.
Unbelievably, there is actually a bit of good news, the Autopilot hasn’t tried to run away, and the plane hasn’t pitched either up or down like crazy. Too bad, that’s a problem the pilot gets trained on every year – he can find and pull the Pitch Trim Circuit Breaker with his eyes closed. Dredging into long-term memory, the pilot vaguely remembers that there IS an Autopilot Circuit breaker, but that knowledge doesn’t include the location of the aforementioned CB (Its on the second row of CBs aft of the center of the opposite wall of the cockpit – a VERY long reach for the pilot, but this bit of knowledge won’t bubble to the surface until after the plane is parked). There is a solid bit of memory that says the AP is on the Avionics 2 bus, so Mr. Intrepid turns off Avionics Bus 2. Good news, it gets quiet; Bertie is dead. Bad news unfortunately is Comm 2 and Nav 2, the pilot’s HSI, and Attitude and Heading Reference System (AHRS) 2, which for some unknown reason is (was) driving the pilot’s Attitude Indicator, are also dead. Fortunately, there are still three ways of determining where UP is – a “peanut” gyro, which in IFR is about as useful as …well, it’s not very useful, the Attitude Indicator on the copilot’s side, which in IFR makes for a seriously honked up scan, and the real-world horizon out the front window. Good news it was VFR!
At this point the pilot has applied for a name change and has claimed the title of Mr. Flustered, just barely managing to keep from busting his assigned altitude. However, radio comm with Oakland is now working and Oakland hands the flight off to NorCal Approach.
Things are getting better now; the pilot gets a higher altitude and a Class Bravo clearance, so airspace is no longer an issue. There are only a few clouds between the plane and where the pilot thinks Napa is hiding. Successfully locating Napa, logging the ATIS and getting the hand-off to Oakland Center then Napa Tower all go like clockwork – fortunately not the type with the little bird that pops out. Until, that is on the approach, the pilot notices that there is no Angle of Attack indication, which is the normal means of determining approach speed. That went away with the demise of Avionics 2. Attempting to think of a word of greater than four letters our pilot flies final at 90 KIAS, knowing that he’s going to float a LONG way down the runway, but accepting the risk as preferable to coming in too slow in a plane with lots of weight and momentum.
After a very nice (if long) landing, the pilot taxis to transient and lets the (to this point) unaware passengers know that he’s got a few things to sort out before boarding the other people and heading up to Redding. Without going into great detail, let’s just say that there are a lot of hoops through which a pilot flying Part 135 must jump in the case of ANY equipment failure, and unfortunately in this case, not all of them could be negotiated and he had to find alternative transportation for the passengers. After which, he got to fly the plane solo to Mather for service and a new Autopilot.
So, was any of this an emergency? Had it been IFR, absolutely YES. But VFR, it was busier that any of us would like to be, sloppier in terms of altitude, heading, and communication than I would have liked, but it was legal, and even better, it was safe. What if I hadn’t remembered about the AP being on Avionics Bus 2?
All I can say is that things go wrong in airplanes, and sometimes they aren’t the things we train for specifically. That’s why it’s so important to understand how things work so problems DON’T become emergencies.