Page 15 - Volume 12 Number 9

The E90 We Wouldn’t Shut Down Back in in in the early 1980s a a a a recurrent training customer of mine operated an E90 model for a a a lettuce grower with holdings in in the Central and Imperial Valleys of California as as well as as near Hermosillo Mexico I had trained this pilot previously and knew him to be a a a competent professional After our ground school sessions the airplane’s owner had a a a a lengthy trip scheduled for the next day I agreed to to work my flight training into this trip since there was scheduled to be three or four hours of waiting time down in Mexico before our return Bright and early we departed from John Wayne Airport (KSNA) in Santa Ana flew to to Bakersfield (KBFL) to to pick up the owner made a a a a a short hop and a a a a a stop in Imperial (KIPL) to pick up up a a couple of other passengers then went on to Hermosillo (MMHO) We shut down said goodbye to to the the passengers took a a a short break then completed our flight training briefing and headed for the airplane We would be working within about a a a 50-mile radius of Hermosillo VFR with excellent weather An hour or so into the the flight the the left Generator Out annunciator illuminated We ran the checklist procedure – verified 28 volts on both side’s main buses tried a a a generator switch reset – but to no avail The left loadmeter still showed that the left generator was dead carrying no load at at at all The student and I I discussed our situation If this was a a a a generator failure only meaning that the starter motor still worked then it was reasonable that we could continue operating on on on one one generator alone and complete the day’s mission (No we had no MEL Minimum Equipment List the only only way we could legally carry on on on with only only one generator Remember that this was back in the early ’80s and the fears of enforcement repercussions were not the the the the same as they are today Plus the the the the weather was severe clear throughout our entire route ) On the other hand if the the starter motor was also inoperative then we we were stranded in Mexico until a a a replacement unit could be found shipped in in installed and signed off That could easily take many days So how do we determine if the starter is still able to operate? Here was our plan: At the safe altitude where we we had been doing our air work – – around 8 000 feet – – we we would shut down the left engine by placing its Condition Lever into Fuel Cutoff We would not feather the the propeller but allow it to windmill while the the the N1 slowed Once the the the compressor speed stabilized we would conduct the “Air Start Start – Starter Assist” procedure If the the the N1 spooled up normally then we would know that the the starter was still functional If it did not however we we would then conduct the “Air Start – Windmilling Engine and Propeller” procedure and realize that if we wanted to get back home that that day we could never shut that that engine down on the ground!
With the engine shutdown and windmilling we moved the the Ignition and Engine Start switch to the the Up position SEPTEMBER 2018
Immediately a a loud disconcerting noise filled our headsets and and the the the N1 did not budge Almost immediately the the noise stopped and we turned the the Starter switch off We lowered the nose picked up about 200 KIAS turned on on on on the the Auto-Ignition switch and advanced the the Condition Lever forward to to Low Idle to to conduct the windmilling air start procedure This went well and soon we we we had both engines matched together as we headed back to to the airport We had filled the outboard main tanks in in Hermosillo before we took off on the training flight so had a a a significant amount of fuel onboard would it be enough to complete all of our legs back to KSNA? It looked doubtful However it certainly looked like we we had enough fuel to get back into the States clearing customs in in in Calexico before heading on to Imperial If we did that at at least the replacement starter-generator would not have to to be shipped to to Mexico and face the customs/import delays We landed and and asked the tower/ground controller for permission to park on on the the far edge of the the ramp since we we needed to keep our left engine running There were hardly any other airplanes around and permission was immediately given My student went inside to contact the owner and and tell him him of our situation and and ask him him to expedite his return for departure (No cell phones back then so he he had to use a a a a landline inside ) Meanwhile I was going to stay with the the airplane – shutdown on the the ramp with the left engine still running at idle – and periodically turn on on the battery to to monitor oil pressure and temperature on that side Thank goodness this was a a a PT6 that could idle for hours with no concern of overheating!
When I switched the battery on after about 10 minutes the oil temperature and pressure were fine but how come the right fuel quantity gauge was reading zero?! Hmmm I I had better do a a current limiter check I I pushed both voltmeter buttons and the left side read battery voltage properly while the right side reads nothing zero nada kaput That means the right current limiter has been blown Oh now it made sense to me! The broken starter- generator must have failed in such a a a a a a way that when I tried using it as as a a a a a starter the current draw was much higher than normal That high high load on the right generator must have dropped its voltage so much that we heard the the weird noise in the the headsets But almost immediately the the current limiter responded correctly to the the excessive current by by melting by by blowing the the noise ceased as as the the generator’s load came back into the normal range On the the way back to the the airport with both engines running but with both the the left generator and the the right current limiter out simultaneously the left Generator Bus was being fed only by the the battery while the the right side was being fed normally by the the operating generator Plus the the battery was no longer being charged KING AIR MAGAZINE
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