Intermittent Issue with IAS/IAS Prof
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I'm trying to narrow down how to reliably reproduce it, but I suspect it has to do with being within 1000ft of a target altitude and/or ALTS mode.
I have had an issue intermittently on several flights with 1.1 (and maybe 1.0, as well). I will engage IAS mode while climbing, however the FD/AP will simply level the aircraft instead of climbing and let the speed increase from the set target. I believe it has happened when I have been nearing an initial assigned altitude after takeoff, right around capture, before increasing the target altitude and engaging IAS/IAS Prof to climb to a higher one.
After takeoff at KBNA my last flight, I had 4000 as my target altitude. I took off in HDG/GA mode, and around 1000ft or so I switched from GA to IAS. While I was sorting the vectors to my first RNAV waypoint, I crossed 3000ft, which reminded me to increase my set altitude from 4000 up to 15000.
IAS showed engaged, but I discovered that the aircraft was not climbing, and the speed was increasing over my set target of 180. I fiddled with several modes, but I needed V/S mode to get me climbing again. Initially, this was just the FD, as I was hand flying, but of course when I engaged the AP the issue persisted.
While climbing, I was messing with the target altitude in order to try to solve the IAS issue and get it working right again, and I heard the chime as it approached my then setting of 12100. I increased the altitude again, and this time when I engaged IAS it started working properly. I'm about to do a second flight and see if engaging/reengaging IAS around altitude capture results in the same issue.
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Just had it happen again, again on the first flight. I was cruising at only a few thousand feet, surfing under a class B, climbing slowly in VS mode. I cleared the Bravo and switched to IAS mode, and she leveled out on me and stopped climbing.
Maybe it has to do with having a preset speed set before first engaging it? I dialed in 220 knots on the IAS gauge before switching from VS to IAS mode. When I turned off the selection on the IAS gauge and then enabled IAS mode it started working fine.
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That's it! I can repeat it. I was cruising at 13500 and set my new target to 15500. I engaged VS mode with a token 500, then dialed in 200 knots and engaged IAS. She leveled out on me.
@Black-Square Nick do you mind taking a look at this? It seems that having a preset speed dialed in before engaging IAS mode will sometimes break it, at least if you're in VS and then try to go to IAS.