Going beyond TBO.
07-14-2018, 01:57 PM
#1
Gets Weekends Off
Thread Starter
Joined APC: Apr 2010
Posts: 291
Going beyond TBO.
Lot of airplanes out there past TBO. I spend time looking around AeroTrader and Controller, and having never owned an airplane myself, I'm surprised at how many owners go past TBO.
Why do owners do that (aside from being cheap).
What would an insurance adjuster have to say in the case of a mishap?
What would a DPE say if you were training in one and brought it to the check?
Just crowdsourcing some knowledge.
Why do owners do that (aside from being cheap).
What would an insurance adjuster have to say in the case of a mishap?
What would a DPE say if you were training in one and brought it to the check?
Just crowdsourcing some knowledge.
07-14-2018, 02:40 PM
#2
Disinterested Third Party
Joined APC: Jun 2012
Posts: 6,023
Originally Posted by BFMthisA10
Lot of airplanes out there past TBO. I spend time looking around AeroTrader and Controller, and having never owned an airplane myself, I'm surprised at how many owners go past TBO.
Why do owners do that (aside from being cheap).
What would an insurance adjuster have to say in the case of a mishap?
What would a DPE say if you were training in one and brought it to the check?
Just crowdsourcing some knowledge.
Why do owners do that (aside from being cheap).
What would an insurance adjuster have to say in the case of a mishap?
What would a DPE say if you were training in one and brought it to the check?
Just crowdsourcing some knowledge.
Does it have any applicability outside of 135 operations?
Do you understand what on-condition means?
07-14-2018, 03:30 PM
#3
Gets Weekends Off
Joined APC: Aug 2013
Posts: 445
My engine is due to be overhauled going by the calendar (although way short on hours). It runs great and compression measures good, so why would I spend thousands of dollars to exchange my good running engine, for a good running engine that could potentially develop an issue due to a mistake by an A&P?
07-14-2018, 04:38 PM
#6
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Joined APC: Jun 2012
Posts: 6,023
TBO is not the number that most believe. It's not like a "best by" date on a carton of milk (which is also not a hard number). It's not an expiration number. It's a guestimate by a manufacturer, and it's a floating number: it's subject to change. It's also only significant for a first-run engine. Once overhauled, all bets are off, and in reality, the way the engine is operated prior to TBO means that it may or may not make TBO It may also run just fine well beyond TBO.
I find that most don't understand the significance of TBO, and fewer understand the meaning of "overhaul." An overhaul can be nothing more than an inspection of the engine and the finding that it's still in tolerance. Do you think that an engine with that level of "overhaul" will go another complete TBO-interval? Unlikely. With that in mind, TBO loses meaning in terms of predictability of future performance, and the reality is that it is no predictor of performance prior to the first overhaul, either.
I have been involved in shops and operations in which we increased the TBO for a particular engine, 50 hours at a time, by running to TBO, performing a teardown, and showing that our maintenance and overhaul permitted continued operation; we did this repeatedly to expand the TBO envelope such that the engine was operable for longer intervals in operations that are TBO-restricted (eg, 135). Conversely, I've many engines never make TBO, and many other that were still strong at TBO.
Consider the concept of the "top overhaul," in piston engines, which can mean a lot of inconsistent things, and offers no assurances, and consider how that impacts TBO (or doesn't). The issue is not nearly as clear as one may think, and far more complex.
In English, please.
I find that most don't understand the significance of TBO, and fewer understand the meaning of "overhaul." An overhaul can be nothing more than an inspection of the engine and the finding that it's still in tolerance. Do you think that an engine with that level of "overhaul" will go another complete TBO-interval? Unlikely. With that in mind, TBO loses meaning in terms of predictability of future performance, and the reality is that it is no predictor of performance prior to the first overhaul, either.
I have been involved in shops and operations in which we increased the TBO for a particular engine, 50 hours at a time, by running to TBO, performing a teardown, and showing that our maintenance and overhaul permitted continued operation; we did this repeatedly to expand the TBO envelope such that the engine was operable for longer intervals in operations that are TBO-restricted (eg, 135). Conversely, I've many engines never make TBO, and many other that were still strong at TBO.
Consider the concept of the "top overhaul," in piston engines, which can mean a lot of inconsistent things, and offers no assurances, and consider how that impacts TBO (or doesn't). The issue is not nearly as clear as one may think, and far more complex.
Originally Posted by BFMthisA10
Ok.
Is “On condition” go beyond compression and metal free oil?
Is “On condition” go beyond compression and metal free oil?
07-14-2018, 04:51 PM
#9
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Joined APC: Jun 2012
Posts: 6,023
https://www.ecfr.gov/cgi-bin/text-id...5#se14.1.43_12
Note the differences between overhauled and rebuilt in 14 CFR 43.2(a) and (b):
Contrast that with 14 CFR 43.2(b):
To qualify as overhauled, it the engine, appliance, or component need technically only be inspected and tested, and found in spec; there are many kinds, qualities, and levels of overhaul. Many think it means brought back to new condition, starting over, and it doesn't. That would be rebuilt, and that's something entirely different.
Operating an engine, appliance, or component on-conditions means that it's operated so long as it's in condition to be used safely. If an engine is beyond TBO, on-condition means that we look at it's compression, perhaps an ongoing maintenance and inspection program, spectrometric oil analysis, etc, and as long as the engine is in a condition to continue operating, it is. It keeps operating until it's no longer in condition, whether it's excessive oil consumption, low compression, or tolerance parameters that exceed manufacturer, owner/operator, or other applicable data an make the engine no longer safe, economically viable, etc, to continue operating.
Think of it this way: if you have an engine which is at TBO, but is burning no oil, still has strong compression, and which has seen regular maintenance, conservative operation, and is in every way still a strong engine putting out rated power, and has no signs of excess wear or trend changes on a spectrometric analysis, what does TBO really mean to you? Do you want to go spend 25,000 to 40,000 on a new engine or spent 20,000 on an overhaul for a perfectly functioning engine?
Suppose the engine is at a calendar interval, but has only flown half of the TBO-recommended hours? (TBO is a recommendation, outside of certain operations such as 121 and 135). Do you really want to spend the money to tear into or replace that engine when it's not close to the hours-TBO? Some engines operate on cycles rather than hours, or both; what if the engine is cycled out but has plenty of hours, or is out of hours or has plenty of cycles remaining?
Most engines have 5 year replacement cycles on hoses, seals, lines, etc, in the engine, but few out side of 121 and 135 operations actually observe those, save for professional operations. I've seen a lot of hoses that ought to be replaced, including oil and fuel lines. The owner might feel that the engine is only half-way to TBO, and feel a false sense of security, yet may be prime for an inflight fire due to a hose failure.
Engine oil should be changed on both an hourly and calendar interval in piston engines; many either have no idea about calendar intervals or don't follow them. Acids collect in oil whether the engine is run or not, leading to corrosion around journals, bearings, lifters, etc, and an engine can experiencing considerable wear or damage just by sitting. One of the worst things that can happen to an engine is allowing it to sit idle for long periods without complete preservation (which includes removing the oil). Such an engine may be in need of overhaul, replacement, rebuilding, etc, long before TBO is ever reached. Again, the issue is complex and one needs to look at the specific engine and circumstances that apply to it.
Note the differences between overhauled and rebuilt in 14 CFR 43.2(a) and (b):
§43.2 Records of overhaul and rebuilding.
(a) No person may describe in any required maintenance entry or form an aircraft, airframe, aircraft engine, propeller, appliance, or component part as being overhauled unless—
(1) Using methods, techniques, and practices acceptable to the Administrator, it has been disassembled, cleaned, inspected, repaired as necessary, and reassembled; and
(2) It has been tested in accordance with approved standards and technical data, or in accordance with current standards and technical data acceptable to the Administrator, which have been developed and documented by the holder of the type certificate, supplemental type certificate, or a material, part, process, or appliance approval under part 21 of this chapter.
(a) No person may describe in any required maintenance entry or form an aircraft, airframe, aircraft engine, propeller, appliance, or component part as being overhauled unless—
(1) Using methods, techniques, and practices acceptable to the Administrator, it has been disassembled, cleaned, inspected, repaired as necessary, and reassembled; and
(2) It has been tested in accordance with approved standards and technical data, or in accordance with current standards and technical data acceptable to the Administrator, which have been developed and documented by the holder of the type certificate, supplemental type certificate, or a material, part, process, or appliance approval under part 21 of this chapter.
§43.2 Records of overhaul and rebuilding.
(b) No person may describe in any required maintenance entry or form an aircraft, airframe, aircraft engine, propeller, appliance, or component part as being rebuilt unless it has been disassembled, cleaned, inspected, repaired as necessary, reassembled, and tested to the same tolerances and limits as a new item, using either new parts or used parts that either conform to new part tolerances and limits or to approved oversized or undersized dimensions.
(b) No person may describe in any required maintenance entry or form an aircraft, airframe, aircraft engine, propeller, appliance, or component part as being rebuilt unless it has been disassembled, cleaned, inspected, repaired as necessary, reassembled, and tested to the same tolerances and limits as a new item, using either new parts or used parts that either conform to new part tolerances and limits or to approved oversized or undersized dimensions.
Operating an engine, appliance, or component on-conditions means that it's operated so long as it's in condition to be used safely. If an engine is beyond TBO, on-condition means that we look at it's compression, perhaps an ongoing maintenance and inspection program, spectrometric oil analysis, etc, and as long as the engine is in a condition to continue operating, it is. It keeps operating until it's no longer in condition, whether it's excessive oil consumption, low compression, or tolerance parameters that exceed manufacturer, owner/operator, or other applicable data an make the engine no longer safe, economically viable, etc, to continue operating.
Think of it this way: if you have an engine which is at TBO, but is burning no oil, still has strong compression, and which has seen regular maintenance, conservative operation, and is in every way still a strong engine putting out rated power, and has no signs of excess wear or trend changes on a spectrometric analysis, what does TBO really mean to you? Do you want to go spend 25,000 to 40,000 on a new engine or spent 20,000 on an overhaul for a perfectly functioning engine?
Suppose the engine is at a calendar interval, but has only flown half of the TBO-recommended hours? (TBO is a recommendation, outside of certain operations such as 121 and 135). Do you really want to spend the money to tear into or replace that engine when it's not close to the hours-TBO? Some engines operate on cycles rather than hours, or both; what if the engine is cycled out but has plenty of hours, or is out of hours or has plenty of cycles remaining?
Most engines have 5 year replacement cycles on hoses, seals, lines, etc, in the engine, but few out side of 121 and 135 operations actually observe those, save for professional operations. I've seen a lot of hoses that ought to be replaced, including oil and fuel lines. The owner might feel that the engine is only half-way to TBO, and feel a false sense of security, yet may be prime for an inflight fire due to a hose failure.
Engine oil should be changed on both an hourly and calendar interval in piston engines; many either have no idea about calendar intervals or don't follow them. Acids collect in oil whether the engine is run or not, leading to corrosion around journals, bearings, lifters, etc, and an engine can experiencing considerable wear or damage just by sitting. One of the worst things that can happen to an engine is allowing it to sit idle for long periods without complete preservation (which includes removing the oil). Such an engine may be in need of overhaul, replacement, rebuilding, etc, long before TBO is ever reached. Again, the issue is complex and one needs to look at the specific engine and circumstances that apply to it.
Last edited by JohnBurke; 07-14-2018 at 05:31 PM.
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