Back in October 2020, Greg Stockman sent in a question to General Aviation News‘ engines expert, Paul McBride, asking about permanently removing a vacuum pump in a Lycoming IO-360-C1C6, installed on a PA-28R-201 Arrow III, built in 1978.
Paul’s answer offer Greg a couple of options for removing the vacuum pump. Now he wants to follow up on that answer with a little more information:
Thanks to a good friend who acts as my “conscience” for my columns, I’ve been advised that I may have mislead Greg and any others who may be thinking about the change he inquired about. This is very important and I hope this information is shared by our readers.
As I stated in my response to Greg, there are no Lycoming Service Publications that cover the removal of a vacuum pump. However, back in the day this type of request was normally discussed with your FAA Principle Maintenance Inspector followed up by submitting an FAA Form 337. This typically was approved in a short period of time and you could proceed with your project.
Now, I’m told that apparently those days are over, and the FAA has taken a different approach. It seems now when you submit the proper paperwork it is reviewed by the regional FAA Aircraft Certification Office (ACO).
I learned a long time ago that, sadly, there is not a lot of consistency among these ACO offices, which has been known to cause some confusion. As an example, one ACO may routinely review and accept your paperwork for removal of the vacuum pump in this case, when a different ACO may reject the very same thing.
My recommendation is that you ask your FAA PMI any questions you may have prior to submitting any paperwork and most certainly before doing any work.
The other important thing I learned from my “conscience” was the fact that Lycoming does not supply the complete vacuum system on any aircraft. It’s true that Lycoming supplies the capabilities for driving the vacuum pump, in addition to several other accessories provided by the original airframe manufacturer, therefore any of those components will be covered in the airframe manufacturer’s Type Certificate for any particular aircraft rather than any of Lycoming’s publications.
Just a quick follow-up question: if any accessory is listed on the Type Certificate, is a Supplemental Type Certificate required to remove it completely?
Would you gain ho by removing the vacuum pump and gears .. I have an O 470 with no use for vacuum .. can I remove it to gain ho?
Thanks
My steam gauges asked me why, though still operating after 60 years of uninterrupted service, they are referred to as unreliable. I didn’t have an intelligent answer.
And they were good enough for Concorde through its lifetime,as well !
At SnF, a friend who owns a 2008 (WAAS G1000) C182 asked my professional opinion about removing the vacuum operated backup instruments and vacuum pump in favor of using the newer Garmin G5’s. My answer pretty much followed the discussion here … it’s not as easy as just swapping out some instruments and removing the pump. Ultimately, it doesn’t matter if it makes logical sense; James Carter is correct. Either there has to be an STC (modifying the TC) or a Field Approval through the ACO.
Subsequently and ironically, I attended a Garmin webinar where they showed removal of all three backup gauges in favor of one new GI 275. Garmin has gone through the expense and trouble of STC’ing and AML’ing that changeover which includes the vacuum pump removal. A STC/AML IS an approved change to a TC/specific airframe. Since they’ve already done the legwork, it’s just a matter of modifying the airplane per the instructions, checking it all out and filling out a 337. No ACO could disapprove it because it’s already FAA approved. That’s why you pay more for these types of installations.
I’m not sure I see the sense in replacing a mechanical backup set of gauges to a totally electronic airplane but … I guess he does? If I owned that machine, I’d keep the thing stock. Now then, replacing the PRIMARY instruments with the more reliable electronic versions in a steam gauge airplane is a different story.
The vacuum pump is connected to the accessory housing and through the magic of gears to eventually place some sort of load on the crankshaft. The crankshaft is balanced and most of the higher powered mouse traps have counterweights that are very critical to the smooth operation of all that rotating mass. By removing the vacuum pump thus changing the load on the crankshaft, are we causing a “Critical” imbalance?? I don’t know, but I would want to know what Lycoming and Continental think about it. I’m assuming the genesis of this question is due to a swap from Steam Gauges to Glass. I’m sure the Avionics Houses have thought about this and should have it all worked out. If not, why not?? My next question is why not keep the Vacuum System as a back up. installed on the right side of the panel?? Have you ever had electrical failure?? Redundancy is good.
If adding or removing Accessories on an engine’s accessory pads were a concern, then you would think that would be a documented warning in the engine’s manual and perhaps even on its TCDS. True that removing, or more, so adding Accessories, impacts the load on the engine and therefore changes fuel consumption. Another reason to remove an unproductive Accessory, better gas mileage.
I think you are full of vacuum.
No bureaucrat ever got fired for saying “no”. Job #1 is keeping the job, so CYA is always the first priority.
Why would anyone think that removal of a now unneeded accessory is a Major Alteration?
If it isn’t need to suck air from something then it is just an unneeded ticking time bomb waiting to come apart, so how could it’s removal be anything but a Minor Alteration needing nothing more than a Logbook entry?
You’re 100% correct Ted, but if the builder (Piper in this case) put the component on the Type Certificate then to remove it you would need to “modify” the TC. I think Paul’s point is that isn’t always easy.
I think you are thinking of equipment list, not type certificate.
Totally agree. aircraft has been modified & approved for return to service with a 337 form filed for new install. The need for a vacuum system has been addressed in said avionics modification. So now you remove the pump, revise the weight & balance & your done. To much bureaucratic B/S as always.