A director of maintenance from Alaska with several King Air B100s called me not long ago. The most recent addition to his fleet had a pressurization problem that would not resolve. The system tested fine on the ground, but there was no pressurization in the air. He had researched the part number of the flow pack in the IPC (Illustrated Parts Catalog), ordered exchange units and installed them. The pressurization checked good on the ground but was “inop” in the air.
I asked him if he exchanged the pneumostats as well, and he had not. That was my first suggestion. My cardinal rule No. 1 with pneumatic flow packs is: Whenever exchanging a flow pack, exchange the pneumostat at the same time.
Assuming that the first set of flow packs were out-of-box failures, he sent them back and ordered an exchange flow pack and pneumostat for each side. He received the parts, installed them in the aircraft, but again, there was no change. Pressurization checked good on the ground but was non-existent in the air.
He called once more, and I admit I was a little bit stymied. I had to dig deeper. I had him make sure all the various components in the pressurization system were working, such as the outflow valve, the safety valve, the dump solenoid and the pre-select solenoid.
Of course he wondered if there was a problem with the controller. It amazes me how many people immediately suspect the controller before everything else. Whenever there is a pressurization glitch, everyone’s knee-jerk reaction is to assume the controller is at fault. When troubleshooting pressurization, the controller is the last place I look – and I do mean last – that’s cardinal rule No. 2 in troubleshooting pneumatic flow packs. These controllers don’t fail. Yes, they can have inaccuracies, especially with selected altitude (being off by 500-1,000 is not unusual) but total failure is extremely rare.
He tested and re-tested the various valves and solenoids to no avail. Everything checked out well. Out of the blue, I asked him for the serial number of this aircraft, and guess what? I knew this B100 quite well! Back when I had my shop, I performed regular maintenance on the King Air for several years.
I asked him if he was ordering flow packs for a -6 engine or a -10 engine. (Note: The Garrett engines originally installed on B100s by the factory were TPE 331-252B-6. Later, an upgrade became available which modified these engines. Installation of the mod turned the engine into a TPE 331-252B-10). I knew this B100 had -10 engines.
I also knew that the flow pack for a -6 engine was not the same as the flow pack on a -10 engine. The IPC he used to research the flow pack only lists the components installed when the aircraft was new. The parts and components that go along with the -10 engines are found in the -10 STC, which would be in the aircraft flight manual.
Once the correct flow packs for the -10 engines were procured and installed, everything worked as advertised. I just wish I had asked more about the aircraft history before diving into discussions of squawk and remedy.
Maintenance Manual Versus STC Requirements
This week, while writing this very article, I got a call from a King Air owner in distress. His model 200 was in a shop for phases and hot sections, and the shop’s estimate raised many questions. He had lost confidence in the shop and wanted my advice. He sent me the estimate, a few photos and the work order. Right away I saw several red flags to pursue.
One of them was an $8,000 charge for brake hoses in conjunction with the 5-year brake hose replacement called out in the maintenance manual (MM). First of all, that amount of money for brake hoses is ridiculous, and it’s what caught the customer’s attention. But way more important was the fact that this King Air had Cleveland brakes! I could see them plainly in the photos. The 5-year brake hose replace does not apply to the Cleveland-supplied brake hoses. It is one of the most common STCs performed on King Airs. The maintenance requirements for Cleveland brakes are in the STC paperwork.
It’s important to note that a King Air with the Cleveland conversion still has two original brake hoses located on the upper and lower struts of the main gear. These hoses are what came with the aircraft; they are subject to MM requirements and they are to be replaced every five years. They cost about a couple of hundred bucks per side.
Remember, all approved aircraft modifications and upgrades come with an STC (Supplemental Type Certificate) which extends the airworthiness of the aircraft’s original type certificate to the modification. The STC is the source for maintenance requirements on that mod; the maintenance manual no longer applies in that area. STC paperwork is normally kept in the Aircraft Flight Manual for easy reference when the aircraft is in for maintenance.
When I called the shop on behalf of the owner, I spoke to two different guys. I asked each why they proposed to perform a 5-year hose change on Cleveland brakes. Both gave me the same blunt answer: “The maintenance manual requires the brake hoses to be changed every five years.” It was delivered in a definitive tone, as if to say “You can’t argue with the maintenance manual so there is no use discussing it any further.” They had side-stepped the whole issue of Cleveland brakes and the STC guidelines.
This was especially odd because, on closer inspection, we found that $8,000 charge was the price of replacing the Cleveland brake hoses! (Note: Cleveland hoses are sheathed with stainless steel webbing; it makes them very durable, so they don’t need replacement every five years; it also makes them far more expensive than regular brake hoses.)
So where do you think the shop found the part numbers for the Cleveland hoses quoted on their estimate? In the IPC? Of course not. The IPC, like the MM, does not apply to STC’d parts. They had to look in the STC.
Questionable shop ethics aside, this owner is now acutely aware of the difference between STC’d equipment versus items original to his aircraft, and he now knows where he, or any shop working on his King Air, must look to ascertain the maintenance requirements – lesson learned.
STC Instructions for 4- and 5-Blade Props
Years ago I had a customer who owned a helicopter charter company. He also owned a King Air C90, and all the maintenance for it was done by his helicopter mechanics (all A&Ps of course.) When he put brand-new 4-blade props on his King Air the mechanics performed the installation and rigged the props according to the maintenance manual.
Unfortunately, his well-meaning mechanics rigged the 4-blade props to the MM specifications for the 3-blade props that had just been removed and were original to the aircraft. They failed to research the STC for the new props.
The mis-rigging was discovered within a year of the installation, but it was way too late. The 4-bade props had to be scrapped. It was a $120,000 mistake. If your King Air has 4- or 5-blade props (whether original to the aircraft or an added upgrade) you should be acutely aware of your low-idle setting and the vital necessity of keeping it at or slightly above the specified setting. If it is too low, a condition known as “reactionless vibration resonance” sets in. If not remedied immediately, the consequences can be catastrophic. In this example, the low idle was set at 900 rpm, as called out in the MM for the original 3-blade props. However, it should have been set at 1,100 rpm in accordance with the STC for the 4-blade prop upgrade – a very expensive lesson learned.
STCs and ICAs
The sustained success and popularity of the Beechcraft King Air has resulted in a vast number of aircraft that are 30 or 40 years old and still going strong. The majority of these King Airs have been modified and upgraded in some way. The applicable STCs are an essential part of an aircraft’s records.
Think of everything you can change or add to a King Air! From engines, propellers and brake conversions to airframe modifications (such as strakes, winglets, wing lockers, etc.) to interior modifications or reconfigurations, avionic upgrades and even conversions to LED lighting. The list goes on and on.
All such modifications were awarded an STC when approval was granted by the Federal Aviation Administration (FAA). When a mod is installed, it comes with STC paperwork, normally kept in the aircraft flight manual. The Instructions for Continued Airworthiness (ICA) is part of the STC. When anyone refers you to the STC for the maintenance requirements of a mod or upgrade, they specifically mean the ICA. All the vital information pertinent to the installation of the mod and the required maintenance tasks going forward are found there. The ICA supersedes the maintenance manual in regard to that mod or upgrade.
Remember, the MM and the IPC only address components original to the aircraft. The ICAs for all subsequent modifications installed on your King Air go hand in hand with the MM and IPC. Taken together, you have everything needed to ensure the continued airworthiness of your King Air.