Hi all,

I thought I'd share my research, findings and knowledge surrounding the Commander 114's STEC 60-2 autopilot. Some of this concerns real world usage (modelled correctly in the sim) and some of it relates to how you use the autopilot in the sim; using either mouse clicks or key assignments / hardware.

General

The STEC 60-2 is a rate-based, analogue 80s development that offers HDG HOLD, NAV HOLD, ALTITUDE HOLD, VERTICAL SPEED SELECT, an (automated) APPROACH mode and REVERSE (backcourse) mode. "Out of the box", the STEC 60-2 does not provide automatic tracking of a GPS flight plan. This means that it will not automatically capture, track and sequence GPS waypoints in a flight plan (whether it is interfaced with a GPS100, GNS 430/530 or newer units like the GTN 650/750). This is because the STEC 60-2, being analogue, does not accept an ARINC input, which all GPS navigators output, for GPS steering. However! Both in the real world and in our Black Square simulated rendition, this problem is easily overcome through the installation of a STEC-901 GPSS converter. This is a small box that sits behind the panel. It takes the ARINC GPS steering signal from the GNS/GTN, etc and turns it into a voltage-based heading error signal, that the autopilot does understand. Depending on the model, some APs need the unit to be kept in HEADING SELECT mode, for this to work (this is simulated perfectly in both A2A's Aerostar and was added to their Comanche, for the native 2024 version). However other models - such as the STEC 60-2 we have here - can accept a heading error signal in NAV mode. This makes the integration of the STEC-901 GPSS converter completely transparent to the pilot. If the GPS navigator is set to "GPS" (and not VLOC), then engaging NAV mode on the autopilot will result in the AP taking the heading error signal and steering the plane along the GPS route.

This caveat around GPS steering means that the STEC 60-2 in the Commander 114 is perfectly realistic and functional, in all featured modes 😎 (ie. there is a STEC-901 behind the panel).

Two unique oddities with the STEC 60-2

1). The unit has no master switch, nor even an AP engage switch. When powered up via the avionics bus, after it has completed it's short self-test, it is always "Ready" (shown on the display) for the engagement of a lateral mode (Heading or NAV). The only additional hardware that comes with it, is the AP disconnect button for fitment to a yoke or stick.

Now, there is a caveat regarding this 'always ready' behaviour that relates to people who use key presses or hardware!

a) If you use a mouse click, when you are ready to engage the AP in the air, you can simply press HDG or NAV and the unit will engage in either of those modes. For vertical control, the unit will hold pitch at the time of engagement. Pitch can be controlled using the 'up' and 'down' buttons. In most cases, pilots will select 'VS' soon after after engaging a lateral mode. This then passes control of the vertical mode up to the "Altitude selector" at the top of the panel. The aircraft will climb or descend at the selected vertical speed (selected in increments of 200fpm, not 100fpm), and will level out at the pre-selected altitude.

b) If you use key assignments or hardware for the 114's autopilot, the autopilot will not engage as above, simply by pressing HDG or NAV. You need to press your assignment for AP MASTER, before then selecting HDG or NAV. This is a limitation with MSFS's core autopilot code, which doesn't support "always ready" autopilots.

2). The second unique oddity with the STEC 60-2 is that it has an "automated" Approach mode. There is no APPR button on the unit and that is because Approach (ILS GS or a GPS GP) is engaged automatically where NAV mode is engaged, and a GS or GP intercept point is reached. It's like magic! Fly an ILS and get yourself onto the localizer in NAV (VLOC) mode. Now, when you reach the GS intercept point, you'll see the unit automatically displays "APR" on it's screen and the aircraft will descend on the glideslope.

One disadvantage of this system is that it's not possible (in NAV mode) to be on a localizer but not enter the glideslope mode. When we used to get cleared for a localizer but not the glideslope yet, we used to keep the AP in HDG mode (to prevent the AP from descending on a glideslope without ATC approval).

TL;DR

• The STEC 60-2 in the BS Commander 114 (and in real life) has no 'ap engage' switch. It is "always ready" and you engage it by pressing HDG or NAV. This can be simulated correctly with mouse clicks but if you use key assignments or hardware, you will need to press your AP ENGAGE button first, before selecting HDG or NAV.

• There is no APR button on the AP. Approach mode is activated automatically if you are in NAV mode and an ILS glideslope or GPS glidepath signal is received.

• The STEC 60-2 does not support GPS steering by default. But we can assume a STEC-901 GPS converter has been installed behind the panel, which provides full GPS steering, for enroute and approach navigation. 😎

Edited 1 hour ago1 hr by JYW

@JYW Great and informative post! Super helpful and appreciated...thanks! 😊

Wow!

Precious info indeed !

Thx!!!