The MLS and VNAV buttons on the MCP are simulated to be inoperative in the RJ Professional, just as they are in the real aircraft.

The MLS button was fitted to the real aircraft during manufacture as a form of future-proofing. At that time, it was believed that Microwave Landing Systems were going to become the new standard for airport approach systems, either replacing or complementing the traditional Instrument Landing Systems at airports around the world. Therefore, it would be beneficial to have the button installed into the aircraft from the day of manufacture to prevent any expensive and time-consuming modifications later in the aircraft’s service life. As it turned out, MLS approaches were only trailed at a handful of airports and they never replaced ILS approaches as they were originally intended, and therefore, the aircraft remains fitted with a non-functional MLS button.

A similar story can be told with the VNAV button. The designers of the RJ expected the aircraft to be fitted with an autopilot coupled VNAV mode at some point within its lifetime. However, as 30 years have now passed since the aircraft’s first flight and it still hasn’t been fitted with a VNAV coupled autopilot mode, it is probably safe to say that it will never be implemented into the real aircraft and therefore, the VNAV button also remains inoperative on the MCP.

Although the RJ does not have any autopilot-coupled VNAV modes, there are still various VNAV functions included within the GNLU-910A FMS, such as the VNAV CLB (Climb), CRZ (cruise) and DES (Descent) pages which provide vertical navigation information including cruising altitude, target speeds, and Top of Climb and Top of Descent calculations.

Some RJ operators also installed an Advisory VNAV (AVNAV) system into their FMSs which displays a VNAV vertical deviation indicator on the EFIS ND on non-precision approaches that have no glideslope. If the VNAV APPR option is enabled in the FMS APPROACH REF page, a flight plan is active and the aircraft is within 2nm of the Final Approach Fix (FAF), the FMS will calculate a descent path using the calculated altitudes at each waypoint on the flight plan and will then display a VNAV vertical deviation indicator on the EFIS ND which the pilots can use as a reference to stay on the correct descent path. As the name suggests, the AVNAV scale only acts as a visual reference to the pilots and does not include any coupled autopilot modes.

For a detailed description of the AVNAV system, please see: https://support.justflight.com/en/support/solutions/articles/17000143398-advisory-vnav-avnav-explained

With no autopilot coupled VNAV mode, climbs and descents in the RJ are performed using LVL CHG (level change) and VS (vertical speed) autopilot modes.

In the climb, it is recommended to use the LVL CHG mode. With LVL CHG mode enabled, the autopilot will control the aircraft’s pitch to maintain the speed selected in the MCP IAS/MACH window. This will ensure the aircraft climbs at the greatest rate possible for the current airspeed and throttle position. It is not recommended to use VS mode for any extended period of time during the climb, as this mode requires constant monitoring of the aircraft’s airspeed to prevent overspeed/stall conditions. The standard climb speed for the RJ is 250 knots to 10,000ft, then 280 knots / Mach 0.66.

In the descent, it is recommended to use VS mode as this provides the most control over the aircraft descent rate, improving passenger comfort, and allows for steeper descents. LVL CHG mode can also be used if desired. Above 8,000ft there are no speed restrictions during the descent for the RJ, therefore, descent airspeed and vertical speed are determined by ATC instruction or the approach procedure. Below 8,000ft, the aircraft is limited to 250 knots by the windscreen bird strike limit.