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because the bypassing air can no longer flow across the oil cooler’s fins. From its market introduction in 1974 until the 1993 model year, the +15°C ice vane limitation was heeded with no operational difficulty experienced.
In 1993, beginning with serial number BB-1444, the B200 incorporated many welcome improvements. Among these were the advent of four-blade propellers as standard equipment, replacing the three-blade Hartzell and McCauleys of the past. The higher low idle compressor speeds and flatter low pitch stop blade angles – required to ensure that propeller speed remained above the new minimum propeller speed limit, a limit imposed to avoid the “reactionless vibration” mode that may lead to propeller damage – conspired to make FOD (foreign object damage) much more likely. Soon after the 300 model made its appearance in 1984, reports began arriving at Beech of numerous cases of first-stage compressor FOD on the PT6A-60A engines used on this new model. The distance from the propeller tip to the ground is less in a 300 than in a 200. Combining that fact with the 300’s pitot cowl and four-blade standard propellers with higher idle speeds, FOD became much too common!
The easy solution was to change the procedure so ice vanes – now correctly called “engine anti-ice” on the
later King Air models – were deployed for all ground operations. The location of the oil cooler in the pitot cowl prevents oil cooling from being negatively impacted due to engine anti-ice activation. Thus, there really was no downside risk associated with this new procedure of “Ice vanes extended for all ground ops.”
Therefore, when this same FOD worry started affecting B200s of 1993 and after design – as well as earlier 200s and B200s that were now being retrofitted with four- blade props – the solution was easy ... copy the 300 technique and use ice vanes all the time while on the ground. Oops! What about that +15°C limit that applies to the 200-series but not the 300-series?
For a few years, the limitation was basically ignored. Personal observation has convinced me that it is extremely rare for oil temperature to hit the maximum redline even in Phoenix, Arizona, in the summer months with a lengthy ground delay. Whew, I am happy for that! Then Beech got around to revising the POH and removing the +15°C limit. Now there is a “Note” in the “Before Engine Starting” section of the normal checklist that reads as follows: “The engine ice vanes should be extended for all ground operations to minimize ingestion of ground debris. Turn engine anti-ice off, when required, to maintain oil temperature within limits.”
22 • KING AIR MAGAZINE
JULY 2024