If you hit the starter switch in your King Air and nothing happens, or if you get a “gen out” light while in flight, starter generators will become top of mind. Generally speaking though, starter generators are not too problematic in most King Airs. The notable exception is the “Infamous -001” found in King Air 300s and 350s (more on that later).
The majority of King Airs flying today use one of three starter generator models. It’s common practice to refer to them by the manufacturer part number (23048-016, -018 and 23085-001) rather than the Beechcraft part number. My apologies to anyone flying a straight 90, A90, B90 or B100, as your starter generators will not be covered here.
Part Number: 23048-016
This is the most common starter generator used on King Airs; it is found on all 200s and B200s, all F90s and later model C90s. It incorporates a wet drive spline. The -016 is not subject to periodic spline lubrication or starter gear checks. For this reason, many King Airs that came with -018s, (early C90s, some E90s, straight 100s and A100s) have had their engines converted to accommodate the 23048-016. This involves installation of a Pratt & Whitney Service Bulletin during engine overhaul. Consequently, there is no benchmark serial number among C90s that identifies which type of starter generator it may have.
Part Number: 23048-018
Model E90s, early C90s, straight 100s and A100s all had starter generator, part number 23048-018. It has a dry drive spline which must be lubricated every 400 hours. The starter generator must be removed so the spline can be lubed. Additionally, the starter gear must be inspected for excess wear using a special tool developed by Pratt & Whitney specifically for this purpose. Failure to perform the drive spline lube on a -018 results in premature wear of the spline itself. If not detected and remedied, the spline will wear out the starter gear inside the accessory gearbox at the rear of the engine. Replacement of the starter gear requires removal of the engine accessory gearbox. This gets very expensive. The 400-hour drive spline lube on a -018 is cheap insurance against this situation.
If you fly a King Air with -018 starter generators, you might want to check your logbooks to verify that both your starter generators are getting the drive spline lube at the required interval. Logic might dictate you look in your engine logs, but starter generators are an airframe item. Although attached to the engine, starter generators are engine accessories and the aircraft manufacturer (Beech) decides which accessories they want to use. Accordingly, all maintenance information regarding starter generators belongs in the airframe book. Maintenance on anything that came with the engine from the manufacturer (Pratt) belongs in the engine logbooks. Starter generators and tach generators are airframe items. Fuel controls and high-pressure fuel pumps are engine items. Unfortunately confusion abounds on this issue. It is not unusual to find airframe information in the engine logbooks and vice versa, so check all your logbooks to make sure you don’t miss anything.
Brushes
Both the -016 and the -018 starter generators are due for overhaul at 1,000 hours or when brush wear is down to minimum. Brushes should last 1,000 hours unless subjected to extreme use. A high volume of starts (as in high-cycle, low-time aircraft) will wear the brushes down faster.
There are those in the field who, if they found brushes worn-out before the 1,000-hour mark, would try to save money by changing the brushes only. In fact, there are some who subscribe to the idea of just changing the brushes until the unit fails completely. Changing just the brushes may be penny-wise, but is pound-foolish.
The problem with new brushes installed in the field is that the brushes won’t seat properly. New brushes have a straight edge but the armature is contoured. This makes the contact between the brushes and the armature very poor. Severe arcing at startup and at altitude is the result. Arcing burns up the armature and pits the new brushes. A vicious cycle ensues: the armature and the brushes degrade rapidly in their fight to obtain a better fit together. So the effort to save money by rebrushing the starter generator only serves to hasten the failure of both the brushes and the armature.
The brushes on your starter generators are checked at every phase inspection. Whenever I found brushes worn down before the 1,000-hour mark, I would overhaul or exchange the unit at that time. It’s important to know that an overhauled starter generator comes with new brushes that have been properly seated (contoured) to the armature. This is done through the use of specialized equipment that spins the armature without putting current to it, and it can take many hours.
Overhauls and Exchanges
If you shop around, you can find an exchange -016 for as little as $1,200. My sources in the industry tell me that $1200 barely covers the cost of changing the bearings and brushes on the core units they receive for overhaul. Keep this in mind when it comes to core charge bill-backs. If the core unit you send back needs anything beyond bearings and brushes, you will get a bill-back on that core. I remember a pair of -016s I sent in for overhaul – one needed a new end bell and the other needed its armature completely re-wound. The overall cost was double the exchange price. This is par for the course with starter generators as the rotable pool ages.
If I were to come across a low-time King Air with starter generators approaching 1,000 hours for the first time, I would recommend overhaul providing the owner could afford the added downtime. I hate to see a relatively new unit tossed into the rotable pool in exchange for one that’s been around the block many times, barely meets minimum specs, and will probably need a new armature (or more) at the next overhaul, providing it makes it that far.
The Infamous Part Number: 23085-001
The starter generator found on King Air 300s and 350s is Part Number 23085-001. It is very similar to 23048-016, but for some reason the bearings in this particular model tend to fail early. And when a bearing fails, the unit destroys itself – hence the “infamous” description.
The 23085-001 has the same 1,000-hour overhaul interval as the other units discussed, but in my experience, very few of them make it. For this reason, I always advised my 300 and 350 customers to exchange or overhaul their 23085-001 starter generators at around 600-700 hours.
When a -001 goes, it is always at the most inconvenient moment – you’re on a trip and you need to fly. You call around for exchanges only to find there are none available! Now you must search for a unit to buy outright for $12,000-$15,000.
But let’s say you find an exchange for $3,000. You need it immediately. In the crate it weighs 50-plus pounds and costs $600 for overnight shipping service. Then there’s the labor to remove and replace the unit on short notice at outcall rates. Once installed, your core unit goes back to the vendor and is found BER (Beyond Economical Repair). These days, full core value on a 23085-001 can range from $10,000-$20,000. All in all, this is a $25,000 adventure once it is over and done. So, save yourself time, money and untold aggravation by overhauling or exchanging your -001 starter generators early.
One parting shot: In the unlikely event that you have a -001 that makes it to 1,000 hours, it will likely be found BER at overhaul and you will be paying the full core value anyway. That’s just the way it is with this part and it’s one of the reasons why they are suddenly scarce when you are desperate for one.
The only time I recommend that an aircraft owner exceed maintenance requirements and do something early, is because I have seen that it will save money in the long run. I am very respectful of an aircraft owner’s maintenance dollar. I think you will agree that 3,000 ounces of prevention by early compliance is worth the 25,000 pounds of cure needed when you wait until the final hour.