Twotter Revived: MSFS2024 mod for Aerosoft Twin Otter MSFS (2020)

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The goal of this project is to restore the glory of the Aerosoft Twin Otter X Extended (by Finn Jacobsen & team) using the modern systems available in MSFS2024, based on the Aerosoft Twin Otter for MSFS2020 (by Hans Hartmann & team). This project is not meant to compete with Microsoft’s Twin Otter in MSFS2024 (by Hans Hartmann & team), which is built for easy accessibility.

At this point, I’m looking for feedback about performance and features. I appreciate your help!

Note: you will need to have a pristine installation of the “Aerosoft Twin Otter v1.1.1” in your Community folder to be able to install and use the mod. The Marketplace version won’t work.

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Patch notes v2024.2.134

General

  • Fixed regression in the last mod release and restored many missing audio events.
  • Fixed regression in the last mod release and restored the aircraft interior from the outside view.
  • Made initialization detection more robust (fixes: TurbSim frequently failing on runway start).
  • Performance optimizations.

KAP 140 autopilot

  • Lateral and vertical mode logic moved from the JS gauge into CBDHC6 WASM subsystems, and every external entry path (faceplate, secondary AP panel, hardware AP panels, FSUIPC, SimConnect clients) now funnels through the same state machine.
  • APR pre-arm removed.
  • “No Auto-ARM” now refuses to arm “behind” the aircraft. If the bug is in the past relative to current motion (>100 ft gap, >50 fpm against the bug), ARM is rejected. Without this guard, ARM was collapsing the rolling alt-target back to the displayed value and reversing FLC’s commanded direction.
  • GS capture clears ALT ARM.
  • GS display is gated on APPROACH HOLD.
  • FLC engage now pins selected IAS for 3 s in the right block.
  • Post-PFT Baro reminder accepts external events.
  • HDG-flash state machine moved to WASM.
  • NAV/APR/ALT/BC face buttons emit H-events instead of firing K-events directly.

Annunciators / Glareshield

  • DEAD REC annunciator now also lights on NAV1 cone-of-confusion.
  • Boost pump annunciators now key on FUELSYSTEM PUMP ACTIVE
  • Pneumatic Low Press, 400 Cycle, Fwd/Aft Fuel Low, Aux Battery Active, generator-bus annunciators all rewired to authoritative SimVars/L:vars.

Instruments — gyros, attitude, HSI, ADF, NAV

  • HSI sources unified. Both captain and FO HSI now read from NAV1 (was: FO HSI on NAV2). The standalone VOR2 head keeps NAV2.
  • VOR cone-of-confusion modelled. Work in progress. Disabled in this build, because it doesn’t look realistic yet.
  • ADF noise model rewritten.
  • KI 227 ADF card now slaves to the gyro. Default behaviour: card follows DHC6_GYRO_{CPT,FO}_HEADING; the HDG knob nudges the gyro card directly (KI-227-01). New EFB option “Disable ADF Card Slaving” reverts to the legacy KI-227-00 manual-knob path.
  • Gyro slaving rewritten as a 3-phase state machine (Idle / FastSlave / SlowSlave) per KI-525A PG p. 31. Fast-slaves at 180°/min until aligned, then trims at 3°/min.
  • Attitude indicator off-power roll drift added. WIP.

Parking brake

  • Made “realistic parking brake” mode more robust.

EFB

  • Made splashscreen more robust.

Sound

  • Boost-pump audio now keys on FUELSYSTEM PUMP ACTIVE.
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Thank you for resolving the LOD issue. The interior appeared transparent in the exterior view. I had assumed this was a bug that occurred when running a 2020 model in 2024.

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Nah, this bug was all mine.

I felt that in an aircraft of this vintage, some of the bulbs behind the glareshield annunciators might be near the end of their lifespan or already burned out, resulting in variations in brightness of the annunciators. So I added an override for a file that defines the interior to add a “bulb age” factor, generated individually per variant. Since that file was no longer part of the base model, but now part of the mod, the sim applied different rules to it (I think), and culled the interior whenever the camera was more than a few meters from the model.

I didn’t notice this issue for weeks. The interior was visible when the walkaround started, and I was so focused on my work on gauges and systems that I always immediately entered the cockpit. Only after releasing the first v2024.2.x version, I stopped treating every flight as a test flight, got back to my “normal” flying (mostly sightseeing while doing FSE jobs), and only then I noticed the holes in the model.

Funny story: I was looking for the underlying issue in all the wrong places, then I decided to ask for help on the dev forum, and minutes after explaining the issue there (and claiming I didn’t override anything related to the visual model) I remembered that innocent change to the annunciators. (They call this “Rubberducking”, and it works.)

I removed the critical file from the mod, moved the bulb age to a different place and the interior was back.

I still don’t know how to get the pilot avatars to show, though.

If you notice any other regressions from the base model, please let me know. Working on X, I might break Y and Z, and never notice. If it’s not listed in the README.md as a “known issue” (and, ideally, if it’s reproducible after a sim restart), I want to hear about it. :smiley:

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Hi @aurel42de ,

I’ve managed to install the MSFS2020 version of Twotter via Aerosoft One and also installed your mod. I need a bit more time to test it, so probably tomorrow, but from what I saw it looks very promising and I can’t wait! A question… any plans to make a radio swap possible for TDS GTNXi unit?

Thanks again for your work!

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I don’t know whether/how this is possible without overhauling the whole mod so it turns the base model into a pseudo-modular aircraft that can make use of SimAttachments.

I tried this, just so I could have a non-default png on the world map, but it triggered some unexpected behaviors in the sim, so I abandoned that approach.

If there is an example of a mod that adds avionics to a MSFS2020 aircraft in a way that works in MSFS2024 (and doesn’t involve modifying the assets of the base model), point me to it, so I can figure out how to do it. If not, this feature might have to wait until someone (possibly me, if nobody else volunteers) mods the MSFS2024 Twotter.

Today? Because I keep telling everybody that it can no longer be downloaded, based on what happens when I try and based on what other people told me. If you downloaded it today (or recently): do you still have MSFS2020 installed on your system? (Maybe that’s the gate that locks me out now.)

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Yes, it’s available in the 2020 branch of Aerosoft One.

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I don’t have MSFS2020 installed since January last year. In Aerosoft One settings it’s possible to define a folder where to install MSFS2020 addons.

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Oh, that’s good news! I confirmed that the Aerosoft One route works for me, too.

I never verified the reports that it was no longer available through Aerosoft One, I just assumed they were correct because it was gone from the web store (it’s no longer on my “Instant Downloads” page, all other products I ever purchased are still there).

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I just added it to 2024 via Aerosoft one at the weekend. What they probably meant was you can’t buy it anymore as a new customer.

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Patch notes v2024.2.134 → v2024.2.142: The Dunce Cap Release aka “TriStar Uncrippled”

General

  • Fixed the EFB tablet running in the background when it shouldn’t, possibly breaking systems in “innocent bystander” aircraft.
  • Fixed the EFB splash screen showing up on runway and in-flight spawns. The Restore button remains reachable from the Debug tab.

KAP 140 autopilot

  • Moved the KAP 140 gauge into a dedicated namespace so it no longer overrides the stock KAP 140 used by other aircraft.
  • Fixed the display sometimes showing “888”/“88.888” characters when starting in a cold-and-dark cockpit.
  • Pressing ARM a second time now correctly cancels the armed altitude.
  • Fixed lateral mode reverting to ROL when cancelling NAV ARM or APR ARM while in HDG mode.

Engines

  • DHC-6-100 series variants moved closer to PT6A-20 specs: ITT peak ~1044 °C (vs 1100 °C on the -27), EGT peak and rated fuel flow scaled to the 550 SHP rating.
  • TurbSim now also follows the sim’s “engine is lit” flag, so failure injection, in-flight flameouts and low-bus igniter cutoffs actually stop the alternate ITT/%Ng simulation from continuing to model a running engine.
  • Added engine exhaust flame and smoke visual effect placeholders. WIP, not hooked up yet.

Fuel system

  • Overhauled boost pumps and fuel selector for more accurate behavior. Restored missing audio, removed conflicting audio.
  • Worked around the sim driving engine-driven fuel pump pressure from shaft (propeller) RPM instead of Ng. The pump is now hard-off below 35 % Ng and ramps back in above 40 %, with a small pressure floor so combustion stays alive with a feathered or near-stopped prop.

Persistence

  • Fixed the “GPS drives NAV1” setting not reliably restoring across flight loads.