Yetti Posted July 28, 2021 Report Posted July 28, 2021 On 7/26/2021 at 9:12 PM, RobertGary1 said: Can’t imagine it’s possible they didn’t have their own AHRS. You wouldn’t be able to put it in hsi mode if it didn’t have its own. Reversion wouldn’t work etc. but I’ve had a dual AHRS failure with two independent 275s. Garmin took possession of the plane for 2 weeks for engineering diagnostics but didn’t give any specific answer to either. It took a lot of posts to get to someone saying a big failure with 2 new instruments. 1 Quote
RobertGary1 Posted July 28, 2021 Report Posted July 28, 2021 1 hour ago, Yetti said: It took a lot of posts to get to someone saying a big failure with 2 new instruments. It’s why I’m also putting a new vacuum pump in. Those who remove their vacuum system and rely solely on a pair of 275’s or G5’s are crazy to me. Quote
Yetti Posted July 28, 2021 Report Posted July 28, 2021 15 minutes ago, RobertGary1 said: It’s why I’m also putting a new vacuum pump in. Those who remove their vacuum system and rely solely on a pair of 275’s or G5’s are crazy to me. The Skyview can have a redundant ADHARs and it selects one as primary one as secondary. And then you have the D10A which is completely separate with separate battery. It seems that G and the FAA are pushing the bounds by not requiring some level of differential redundancy 3 Quote
RobertGary1 Posted July 28, 2021 Report Posted July 28, 2021 18 minutes ago, Yetti said: The Skyview can have a redundant ADHARs and it selects one as primary one as secondary. And then you have the D10A which is completely separate with separate battery. It seems that G and the FAA are pushing the bounds by not requiring some level of differential redundancy I’m not sure I follow. In the Garmin set up the attitude indicator and hsi each have an AHRS and if one fails it auto reverts to the other. Well software bugs aside. Quote
Yetti Posted July 28, 2021 Report Posted July 28, 2021 7 minutes ago, RobertGary1 said: I’m not sure I follow. In the Garmin set up the attitude indicator and hsi each have an AHRS and if one fails it auto reverts to the other. Well software bugs aside. The Skyview screens are on a network. The AHARS is part of the network. So the screens get to decide which one is primary. In the case of the the 275 Each has a AHARS and if the software fails it will fail the same way in each unit. and now you have two dead units. The Dynon would still have the Dynon D10A as one more back up. Quote
RobertGary1 Posted July 28, 2021 Report Posted July 28, 2021 1 hour ago, Yetti said: The Skyview screens are on a network. The AHARS is part of the network. So the screens get to decide which one is primary. In the case of the the 275 Each has a AHARS and if the software fails it will fail the same way in each unit. and now you have two dead units. The Dynon would still have the Dynon D10A as one more back up. Garmin has a database and the AHRS in both GI-275's as well as air data is shared and the unit warns you if there is a disagreement. But they are running the same software. The software on my backup vacuum attitude is pretty simple -Robert Quote
whiskytango Posted July 28, 2021 Report Posted July 28, 2021 On 7/26/2021 at 6:14 PM, Ragsf15e said: I didn’t find it hard to believe either. Damage from overloading the airplane (speed or Gs) doesn’t happen exactly at the published limits. I don’t see the airplane coming apart 1 kt or 0.1 G over the limits, but at some point damage starts to happen. Maybe invisible at first, but increasing with continued stress until things become noticeable like the popped rivets and leaking fuel. In the F-15E (yes, it’s designed a little differently but the same principle), we had had Level 1-5 for Over Gs. Level 1 just requires an inflight battle damage check by your wingman, then continue. Level 3 might require declaring an emergency and an exterior maintenance inspection. Level 5 requires all of the above plus the pilot buying the crew chief a case of beer and helping him remove every single inspection panel on the airplane. I think the guy did great by somehow not pulling 8 Gs when he saw the ground coming up through the haze. That might have initiated uncontrolled disassembly. This raises several questions. Is it possible for an IA doing an Annual on this M20F, who is not aware of what occurred, to tell that it has been subjected to an over-stress condition simply by pulling all of the inspection panels and looking at the aircraft? What would the IA look for - broken or deformed fasteners, or structural components that do not have the correct dimensions due to plastic deformation, etc? Can metallurgical or load testing be done on structural components to determine if the factory +/- G ratings and the Va, Vne speeds are still valid? It would be interesting to see what airframe logbook entry was made (if any) after this incident. 1 Quote
takair Posted July 28, 2021 Report Posted July 28, 2021 21 minutes ago, whiskytango said: This raises several questions. Is it possible for an IA doing an Annual on this M20F, who is not aware of what occurred, to tell that it has been subjected to an over-stress condition simply by pulling all of the inspection panels and looking at the aircraft? What would the IA look for - broken or deformed fasteners, or structural components that do not have the correct dimensions due to plastic deformation, etc? Can metallurgical or load testing be done on structural components to determine if the factory +/- G ratings and the Va, Vne speeds are still valid? It would be interesting to see what airframe logbook entry was made (if any) after this incident. I’ve not come across a Mooney that I’ve known to exceed limits, but I have come across at least one Bonanaza….a new at the time 36. Similar scenario…Vne exceedance with hard pull out. In that case the wing and tail were no longer in alignment…very visually noticeable and there was oil canning on the fuselage and surfaces. It was “totaled” , but I believe someone picked it up and rumor was that they got it flying again. Popped rivets are also a clue. The problem is when they don’t completely pop, but have some sheer. I think that on a Mooney, things to look for would be unusual oil canning and the wing and tail being out of alignment. 3 Quote
Vance Harral Posted July 29, 2021 Report Posted July 29, 2021 3 hours ago, whiskytango said: Is it possible for an IA doing an Annual on this M20F, who is not aware of what occurred, to tell that it has been subjected to an over-stress condition simply by pulling all of the inspection panels and looking at the aircraft? I don't know the answer to that question, but I do know the one airplane I've seen subject to an over-G condition (a high wing Cessna) had misaligned wing halves and oil canning on the wing skins. The damage wasn't so significant as to be grossly obvious to a casual observer, but it wasn't difficult to see if you just stood about 20 feet away from the airplane and gave it a decent eyeball look. The lesson I took away from that is, make sure your pre-flight inspections include "big picture" looks at the airframe. I see a lot of pilots get so focused on inspecting individual nuts and bolts that they could easily miss the entire empennage or wing structure being bent. 1 Quote
EricJ Posted July 29, 2021 Report Posted July 29, 2021 3 hours ago, whiskytango said: This raises several questions. Is it possible for an IA doing an Annual on this M20F, who is not aware of what occurred, to tell that it has been subjected to an over-stress condition simply by pulling all of the inspection panels and looking at the aircraft? What would the IA look for - broken or deformed fasteners, or structural components that do not have the correct dimensions due to plastic deformation, etc? Can metallurgical or load testing be done on structural components to determine if the factory +/- G ratings and the Va, Vne speeds are still valid? It would be interesting to see what airframe logbook entry was made (if any) after this incident. There is some published guidance on the topic which I can't find at the moment, but there are clues like loose rivets, panels that are warped, sheet metal seams that bulge or no longer fit tightly, etc. For many airplanes there are dimensions that can be checked with a tape measure to assure that things are still where they're supposed to be relative to each other, etc. Some of these things, like a displaced panel seam, loose rivets, etc., might be easy to spot even if you weren't looking for them, but otherwise it's probably unusual for somebody to get the tape measure out during an annual and make sure the airplane is still square. If there was a known overspeed or overstress event, then those are likely the sorts of things that would be done. I thought I saw somewhere that the airplane in this incident had new tank leaks, and the gear needed adjustment, which would certainly indicate that some closer attention was warranted. 1 Quote
carusoam Posted July 29, 2021 Report Posted July 29, 2021 The cool thing about metal planes… they can flex, a lot! Then unflex back to normal… millions of cycles… There is a limit to how much they can flex, before they yield… Once they yield, they don’t bend back… They will only yield so much, before they break… So…. Bending a plane enough to cause a fuel leak… isn’t all that hard… taxiing over rough surfaces can make this happen with aged sealant… I have only seen one bent plane… A retractable Cherokee… I brought it in for a PPI… My mechanic noticed a bunch of overstress signs as he walked towards it… That poor plane was the victim of a repeat offender… the bondo that was supposed to hide the oil canned sheet metal was popping off…. It had a few broken rivets that were just hanging in their holes… my mechanic pulled one out to show me… The owner and I flew once… the landing was very solid… I think the Earth said ouch… Some people like to stall their planes a tenth of an inch above the pavement… other like to fly their plane onto the surface… this fine gentleman preferred a subcutaneous approach… An over stressed plane will be easy to recognize by a knowledgable/familiar person… that is an important part of the PPI… Over speeding a plane is not usually a stressful event… until the next event occurs… like you bump into some turbulence… or need to change course… above Vne… If you jump into a new 2U plane and it has a pair of GI275s… be sure you know what the back-ups are… all GI275s look alike… but, there are a myriad of expensive options that are required to make them work as you might expect in an emergency… PP thoughts only, not a mechanic… Best regards, -a- 1 Quote
PT20J Posted July 29, 2021 Report Posted July 29, 2021 I’m putting in a G3X / G5 system next month. The problem with one primary and one backup is that it, short of a gross failure, it can be difficult to quickly figure out which AHRS is wrong especially under pressure. I thought about keeping the vacuum system and KG 258, but that’s a lot of stuff to maintain. I looked at electric backup gyros, but they are all pretty pricey given that I’m looking only for a tie breaker for a (hopefully) very unlikely failure mode. I finally decided to put in a AV-20-S. It’s NORSEE approved, only 2-1/4” dia., and at $895, it’s cheap. And, who knows, maybe I can even get the AOA function to work. I don’t need most of the functions, so I’m not adding the OAT probe. Skip 3 Quote
Yetti Posted July 29, 2021 Report Posted July 29, 2021 There is this story of a Mt. Denali sightseeing plane that got caught in severe turbulence and made a mess of the plane. I wish I could find it. It was fascinating. And I think he flew it out and landed it. But upon looking at the plane would have chose otherwise. Quote
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