Page 22 - Volume 11 Number 4

were flown back “home” for the cowling modification and the addition of the auto-ignition switches and torque sensors. I believe that most, if not all, of the straight 90s were also converted on the line to the new style of system ... at Beech’s expense. The Pilot’s Operating Manuals (POMs) were revised to include the requirement to arm the auto-ignition switches in icing conditions, as well as at night above 14,000 feet. The clouds were harder to see at night, of course, and a 2,000-foot buffer zone was subtracted from 16,000 feet, the lowest altitude where engine ice ingestion had been problematic.
With the corrected design of the ice vane system, a pilot who uses the vanes at all times when flying in visible moisture with the OAT at 5° C or below will never experience an engine flameout due to ice ingestion. Thus, his arming of the auto-ignition switches provides no benefit. Peace of mind? Sure. Staying in compliance with the airplane’s POM? Of course. So we will go ahead and arm the switches. But the need for the ignitors to re-ignite the fuel/air mixture the windmilling engine is still providing following a flameout is nil if the ice vanes are properly used.
Glow plugs were replaced with spark ignitors beginning with the introduction of the 200 model in 1974. Thinking that these new types of ignitors would have an almost infinite lifetime as compared to glow plugs, the decision was made – a bad decision, in my mind – to have the 200 operators arm the auto-ignition switches for all flights, all of the time. It did not take long for Beech to realize that the spark ignitors were in fact life-limited. Too many operators reported that they were replacing these new ignitors nearly as often as the old style. Of course, the reason they were failing is that, with auto-ignition armed at all times, the plugs were actually sparking – and wearing the electrodes – whenever torque was low. Silly as it now seems, the first model 200 checklists had the switches armed from soon after start to right before shutdown, so the ignitors were sparking for most ground operation. A POM revision (actually a POH revision, Pilots’ Operating Handbook, since the name and format had been changed by that time) was issued that moved the arming of the switches to the Runway Lineup procedure and the disarming came in the After Landing section. This direction was carried over into the F90 POH upon that model’s appearance in 1978.
Finally, with the appearance of the 300 model in 1984, the Beech checklist writers moved the arming and disarming of auto-ignition back to what it had been in the 90-series: Use for icing conditions and at night when icing conditions may be entered unknowingly.
I would venture to say that most King Air pilots arm auto-ignition when taking the runway on every flight,
even when it is severe clear and warm. I know that some King Air training providers advocate this. If that makes the pilots happy, so be it. Nothing is being harmed by doing so except perhaps slightly more plug wear. To replace a few more spark ignitors during thousands of hours of operation makes nary a ripple in the overall cost of operation. But please realize that the system is useless unless a flameout takes place. Although there have been a handful of reports of engine flameouts caused by something other than ice ingestion – a condition lever cable rigged too close to fuel cutoff, fuel starvation due to mismanagement – these types of situations are extremely rare. I believe that the propensity to arm auto-ignition on every takeoff comes partly from pilots with jet experience, in which the ignitors can provide a relight following bird ingestion into the engine. Make no mistake, however, bird ingestion cannot and does not happen in a PT6 turboprop.
In summary, I will never state that a pilot is in the wrong if he or she arms auto-ignition for every takeoff and throughout the entire flight. But I hope they will accept that their colleagues are also not in the wrong if they reserve auto-ignition usage for icing flight.
Do you recall the windmilling airstart “envelope?” The POMs/POHs state that airspeed must be above 140 KIAS and altitude below 20,000 feet when conducting this procedure. During my years of conducting inflight training, I can verify that the lower the altitude and the higher the speed, the cooler that starting ITT will be, due to more air entering the engine. Although, as I have written here, use of auto-ignition is a rather moot point if the ice vanes are used properly, nonetheless I have pondered the ramifications of having auto-ignition provide a relight following ice ingestion when cruising at high altitudes. I hope none of us have the experience, but my belief is that there’d be an excellent chance of overtemping the engine if auto-ignition provided an automatic relight up above FL200.
Conclusion? Make sure auto-ignition is armed for icing flight but realize that the proper use of ice vanes nullifies the need for the relight that the ignition would provide. KA
King Air expert Tom Clements has been flying and instructing in King Airs for over 44 years, and is the author of “The King Air Book.” He is a Gold Seal CFI and has over 23,000 total hours with more than 15,000 in King Airs. For information on ordering his book, go to www.flightreview.net. Tom is actively mentoring the instructors at King Air Academy in Phoenix.
If you have a question you’d like Tom to answer, please send it to Editor Kim Blonigen at kblonigen@cox.net.
20 • KING AIR MAGAZINE
APRIL 2017