KAP 140¶

Overview¶

The Bendix/King KAP 140 in the Twotter is a two-axis rate autopilot with altitude preselect. It was designed for the entry level General Aviation market. To the best of my knowledge, the KAP 140 is not certified for installation in any twin engine aircraft, let alone in a twin engine turboprop the size of the Twotter.

References¶

Pilot's Guide

Modes¶

Our pimped KAP 140 supports the following lateral modes:

ROL holds the wings level. It's not a bank hold mode.
HDG mode follows the orange heading bug on the Captain's HSI.
NAV mode follows the source selected on the GNS 530.
APR mode follows the source selected on the GNS 530 more aggressively than NAV mode, appropriate for an approach, and arms and activates the GS vertical mode.

Vertical modes:

ALT holds the current altitude.
VS acquires the current vertical speed and holds it.
FLC (IAS on the separate panel) acquires the current airspeed and attempts to hold it: reduce the power and FLC mode will descend to maintain the speed, increase the power and it climbs.
VNV follows the Coupled VNAV path (only if the option is enabled).
GS follows a glideslope or glidepath and is activated as part of APR mode.

I implemented the KAP 140's "Vertical Trim" features, enabling the UP and DN buttons in all vertical modes (except VNV). Short press:

In ALT mode, the altitude to hold will be nudged by 20 ft up or down per button press.

Info

Nudging (short UP/DN presses) in ALT HOLD mode changes the altitude hold reference, while the display keeps showing the altitude alerter reference. To see the effect of the nudge, you will have to check the altimeter; there is no feedback on the KAP 140 display.

In VS mode, the UP/DN buttons control the vertical speed in steps of 100 fpm. (That's the one behavior the stock sim KAP 140 implements.)
In FLC mode, the UP/DN buttons control the reference speed (IAS) in steps of 5 kts.

Long presses (click the UP or DN buttons with the mouse and hold the mouse button; if you use hardware controls, ensure they send the _Push and _Release B:events):

In ALT mode, holding the UP or DN button will initiate a 500 fpm climb or descent that is maintained until the button is released. Just as with nudging the altitude, only the internal ALT HOLD reference is changed, the display keeps showing the selected alerter altitude.
In VS mode, holding the UP or DN button will increase or decrease the vertical speed by 300 fpm per second.
In FLC mode, holding the UP or DN button will increase or decrease the reference speed by 15 kts per second.

Operation¶

On power-up, the unit runs a preflight test, which ends with the display test (all display elements lit). When the PFT is done, the pitch axis is locked out for about 30s, indicated by a blinking red "P". Simultaneously, the unit waits for the blind encoder to reach operational temperature, which, in cold conditions, can take up to three minutes. This is indicated by dashed lines in place of the alerter altitude.

Note

The real unit has a red warning light for pitch lockout, separate from the display. This light isn't which isn't present in the visual model. The blinking red "P" is a workaround, specific to the mod.

When you engage the autopilot, it will default to ROL and VS, it will keep the wings level and maintain the current climb or descend.

Info

ROL is not a bank hold mode, it's a wing leveler.

Disengaging the autopilot will flash the AP annunciator for five seconds.

Arming NAV, APR, or REV flashes the HDG annunciator for a few seconds as a reminder to use HDG mode to set up the aircraft for intercept.

Intercepts beyond about 45° are not recommended.

When the autopilot is engaged and you select a different altitude, capture will arm automatically, indicated by ALT ARM.

Warning

If the autpilot is not engaged while you pre-select an altitude, it will not show ALT ARM. It will also not arm the capture when you engage it, and it will happily blow through the selected altitude. If you want the AP to capture the altitude, you need to press the ARM button or change the altitude while the AP is flying.

1000 ft from the selected altitude, the altitude alerter sounds an alert, the annunciator comes on, and if enabled, you'll hear an "Altitude!" callout. Within +/- 200 ft of the selected altitude, ALT ALERT stays off. An audible alert tells you when you're at the selected altitude. If you leave the +/- 200 ft buffer, you'll get another alert and the callout "Leaving altitude!" (if enabled).

A short press of the BARO button shows the altimeter setting for three seconds so you can adjust it with the knob. Holding the button for two seconds toggles between inches and hectopascals.

Voice callouts¶

According to the manual, the KAP 140 has a few voice callouts which play on the intercom (as opposed to the "beeps" which play over the cockpit speaker). I could not find any reference, so I don't know what they sound like. Consider the present set of samples a placeholder. Two trim warnings are unconditional, the other three messages are optional and whether they play is either decided when the unit is certified for an airframe or when the unit is installed in the airframe (not sure). In the mod, they can be enabled on the EFB Config tab.

"Trim in motion" when the autopilot has been running the pitch trim one way for five seconds, and the trim is already well out
"Check pitch trim" after fifteen seconds of continuous one way trim, with the PT annunciator flashing an arrow the way the trim is going
"Altitude" 1000 ft before the preselect
"Leaving altitude" 200 ft after departing it
"Autopilot" on disconnect

Warning

The two trim callouts are not notifications, they are warnings telling you that something is wrong.

The voice is currently played simultaneously with the beep altitude alerter beeps and the disconnect signal. Without reference, I cannot say whether that behavior is correct.

Known issues¶

The AP still uses the Captain's HSI baro instead of its own.
Preflight test plays a disconnect signal instead of a completion chime when it ends, reference needed.
The unit engages on a simple press rather than the late-software 0.25s hold, to avoid issues with hardware buttons.
The trim announcements only ever fire on autopilot-commanded trim. The real unit watches the electric trim system; the sim reports one trim position and does not say who moved it, so trimming by hand would otherwise set the warnings off.

Events¶

If you have hardware controls that produce push and release events, you can use B:events to control the UP/DN buttons:

UP: B:AUTOPILOT_KAP140_UP_Push and B:AUTOPILOT_KAP140_UP_Release
DN: B:AUTOPILOT_KAP140_DN_Push and B:AUTOPILOT_KAP140_DN_Release

Reviewed 2026-08-20.