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.

Why? Because we prefer a plane that’s legendary!

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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.

Screenshot 2026-05-11 222310
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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.

Screenshot 2026-05-11 222650
Screenshot 2026-05-11 2226501507×842 72.5 KB
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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.
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Patch notes v2024.2.142 → v2024.3.19

Wear & Tear

  • Vertical slice of a new optional system that ages and damages individual aircraft components. Enable via the Reliability slider on the EFB Config tab.
  • Each glareshield annunciator bulb now has independent age and cycle counts. Bulbs dim continuously as they age and can burn out.
  • Either pitot heating element can now burn out if the heater is left on for extended periods while stationary.
  • A Maintenance tab in the EFB app is active while on the ground with engines shut down and lists every component that has accrued stress or damage. Re-roll will randomize the aircraft state (production year, TTAF, and all component states) and Request Service runs maintenance and produces a per-component report.
  • A Reset button on the Debug tab resets everything to a factory-new state.
  • Wear state persists per variant in the WASM work folder.

Engines

  • Mitigated push-from-idle ITT spike. The Wf acceleration ceiling at low Ng was too loose, allowing quick throttle movements from idle to drive ITT into the red.
  • Added missing smoothing to the ITT needles.
  • Fixed issues that caused both engines to quit during the cinematics on a runway start and, occasionally, one engine to quit after the cinematics completed.

KAP 140 autopilot

  • New EFB Config toggle “Disable Flight Director”. When enabled, the pitch and roll command bars on the attitude indicator are removed; raw autopilot annunciators remain.
  • Work on an overhaul of lateral modes was reverted for this release. But I shall show this AP that I can be its master. I shall perfect my own race of AP modes, a race of atomic super-modes that will conquer the AP!

Electrical system

  • Pitot heat split into two independent circuits. The sim only provides a single pitot-static system that supplies both airspeed indicators. Future work must separate the pitot probes so a single heating element can fail leading to a single airspeed indicator getting stuck.
  • Generators no longer source power with the DC Master in OFF. Fixed cases where generator output reached the bus while the master switch was closed.
  • Changed GPU breaker from 200A to 400A and fixed GPU being disconnected early at engine idle with both generators switched off. This should prevent avionics from rebooting during GPU-powered engine starts.

Cockpit / switches

  • Switches mounted under a protective guard now return to the safe position automatically when the guard is closed.

Avionics & instruments

  • Radio audio panel persists across flights.
  • ADF twilight interference was using garbage data and probably always active, leading to more ADF needle oscillation than intended.

EFB

  • New Maintenance tab (see Wear & Tear above).
  • Reliability slider on the Config tab (Off / Reliable / Unreliable / Not Airworthy).
  • Visible scrollbar added to scrollable content.
  • Disable Flight Director toggle on the Config tab.
  • Debug tab reorganized into collapsible sections (Persistence, TurbSim, Wear & Tear).
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Thanks for this. I’m reading some things here, like bulb dimming, that not even A2A or Black Square do, as far as I know. Unbelievable.

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Thanks for your kind words. I think you’re right, the mod has a few features that go beyond what I’ve seen in other aircraft. I wish the explanation was that I’m a genius, but it’s much simpler than that.

I enjoy freedoms that A2A or BKSQ don’t have.

  • I can waste as much time learning about the lifecycle of a 327 lamp as I want, because I don’t have a deadline or mouths to feed.
  • I don’t have to make sensible decisions about the features I implement or their order, because the base plane is already complete.
  • I don’t need to compromise to keep people happy who don’t RTFM, because I’m not paying support people to handle them.
  • And I don’t need to worry about performance on consoles or potatoes: as long as I can fly the Twotter in VR without stuttering, that’s good enough for me.

And, of course, I’m standing on the shoulders of giants like A2A, BKSQ, FBW, WT: whenever I don’t know how to do something, I get my inspiration from them.

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Patch notes v2024.3.19 → v2024.3.47

Flight model, suspension, AP: CCM tuning

A new flight-model developed by the OG Twotter Modder and Legend CanadianCaptainMoustache (CCM) for this mod is now the default for every base variant. It’s work in progress, but I feel it’s a massive step for the mod. I can’t thank CCM enough for his contribution!
Because this is a quite drastic change towards realism, the (slightly overpowered) old model is available as a per-variant “Legacy tuning” alternative, doubling the number of variants to 26.

  • CCM’s tuning overhauls flight model, flaps, props, steering, and suspension. It hits the numbers, provides more personality to the variants, feels more honest, and gives the Twotter its “stance”, the typical nose-down attitude in cruise and descent.

  • The legacy disking-drag is off for CCM (physics solves disking directly), on for Legacy.

  • Beta-range annunciators rewired to harmonize with CCM’s changes.

ADF realism overhaul (with input from CCM)

The ADF system has been rebuilt from the ground up. CCM’s real-world input and pilot reports drove the calibration.

  • Bank/dip error. Overfly a station in a turn and the needle leans toward the low wing. This falls straight out of the geometry (the loop antenna tilts with the airframe).

  • Quadrantal error. Each airframe carries its own small bearing distortion off the cardinal headings, rolled per session — so no two Twotters read quite identically.

  • In a tight cone directly overhead the station, multipath interference confuses the receiver.

  • Distance and weak signal. More wander the farther out you are; on a fading signal the needle twitches, and on a sustained loss it parks to 90° (“back to the peg”).

  • Night and dusk. Extra skywave wander after dark, driven by the position of the sun.

  • Per-station character. Each NDB feels a little different and drifts gently within a session. This RNG-driven effect is not grounded in physics as such, it stands in for actual effects we cannot simulate because of sim limitations (like terrain, coastal refraction, weather etc.).

  • Real station altitude. The cone now uses the tuned NDB’s actual elevation from the nav database, so a mountain-top beacon behaves differently from a sea-level one.

  • ANT mode parks the needle (per KR 87 manual).

  • Needle freezes in position on receiver power loss. No magical parking without the receiver driving it.

  • Fixed: frequency and modes can no longer be changed while the receiver is off or unpowered.

  • Known issues: the system cannot react to lightning, the sim doesn’t provide the necessary data.

KAP-140 autopilot

New lateral modes are shipped experimentally behind a Config toggle. The default is the existing stock lateral path.

  • New EFB Config toggle “Alternative lateral modes”. When off, lateral AP behaves as before. When on, the AP will (hopefully) stop overshooting (especially when flying near or beyond the polar circles) and capture radials, ILS, and the magenta with less drama.

  • CCM did some AP tuning, I did some AP tuning (thanks to CCM “unlocking” it for me by pointing out that ai.cfg contributes to the AP config). It works, but it probably can use more refinement.

  • More work on the Alternative lateral modes: a more responsive, less wandery heading bug, and less over-banking in turns at low airspeed. Still work in progress.

  • Fixed a long-standing bug that sometimes swallowed Vertical Trim (UP/DN) presses in FLC and VS modes.

  • Fixed FLC mode sometimes showing a vertical speed in fpm instead of a selected speed in kts when first engaged.

  • Known issue: AP still uses Cpt HSI baro instead of its own.

Instruments & controls

  • Calibration errors. Work has started on inducing variations between mirrored instruments (altimeters, HSI, RMI).

  • Snappier HSI knobs. Increased the speed of the HDG bug and the course needle when using the VC controls.

Anti-ice

  • The inertial separator switch now holds in the Retract position for a moment after you let go. Before, it sometimes snapped back immediately without letting the switch animation play out, which looked broken and confused users.

Wear & tear

  • Pitot-heat wear now only builds up when it physically should: warm ambient temps and lack of airflow.

  • Fixed an issue that would keep glareshield annunciator bulbs inoperative even after a maintenance pass.

Parking brake

  • Asymmetric pedal release no longer un-latches the brake. Fixed a long-standing issue that caused the parking brake in realistic mode to only latch when both pedals were released pretty much simultaneously. It should be much more reliable now.

Persistence

  • Fixed: NAV2 OBS jumps to 0° when the user touches the OBS knob for the first time.

EFB

  • The splash now starts in a “Waiting for flight to start” state with no action buttons

  • Added tooltips for config options.

  • New Config toggle “Alternative lateral modes” (see Autopilot above).

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Sincere thanks to both of you for your sterling work bring much needed realism to such an iconic plane. The Twotter has been done a disservice in the recent past, on many fronts, and it’s great to see it is getting the attention it needs, and deserves. :clap::heart_eyes:

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I am amazed every time I see the amount being updated.
Thank you very much for your hard work.