How do I follow an ILS glideslope on the ADI in Falcon BMS?

Question

I'm currently flying the ILS landing mission in Falcon BMS, I'm practicing landing using the instruments (head down) and although I'm mostly OK with the LOC, I struggle to maintain a 2.5 degree glideslope.

In the training doc for Falcon BMS there is the following information:

ADI gives an angular reference to the position of the glideslope. Each dot on the left side of the ADI represents an angle of 2.5°

But I don't know how to achieve the above. I watched some YouTube videos but I didn't see anyone aiming for those dots on the ADI (yet they managed to land perfectly).

I don't want to chase the glide path bar on the ADI, so how do I hold a proper glideslope using the instruments?

Answer 1

The trick to flying a raw-data ILS is to find the pitch attitude that gives you the descent rate that achieves the target glide slope as far out as possible, then hold the attitude as you monitor the ADI, making small attitude changes and waiting for the result when corrections are required.

So try this procedure:

1. As the ADI comes alive in level flight, gradually lower the nose as the indicator approaches the middle index to an attitude that is giving about 6-700 fpm down The required descent rate depends on ground speed - a shallow glide slope like that going 130-140 kt will be somewhere around that descent rate; finding it by trial and error is easy enough (a normal 3 degree glideslope, which you are probably really referring to, will need about 750-800 fpm going that speed). Note the pitch attitude in degrees and hold the attitude.
2. Monitor the ADI. You want it to be very slowly creeping toward the target. If it stops above the target index or starts rising, you are descending a bit too fast. Raise the nose 1 degree on the pitch index, hold the new attitude and wait. Vice versa if the opposite problem. If it keeps moving the wrong way, change the pitch another degree and wait.
3. When the ADI is on the target, pitch a degree to stop it from moving, and wait.
4. At some point with these little tweaks you will find yourself on slope with the ADI not moving. Note the pitch attitude and concentrate on holding that pitch attitude.
5. If the ADI starts to drift up or down, same deal, pitch up or down one degree and wait. If that's not enough, pitch another degree and wait. And so on. The key thing is to keep the corrections small and be patient.

As you get farther down the ILS the sensitivity goes up and the deviations become harder to track so it becomes critical to get sorted out as far out as possible and have the pitch attitude nailed as you get close in. If you have the pitch angle and hold it the slope will generally take care of itself unless you encounter a change in wind that affects your ground speed.

The other thing is trim trim trim. When you are on-target and on-speed, trim to hands off. Now only slight pressures are required to make corrections, and the "default" or relaxed, control input is the nominal correct one.

Answer 2

Am I correct in assuming that you are using the Glideslope Indicator to measure your angle of descent. In other words, the wording of your question makes it sound like you believe the center of your Glideslope Indicator represents an angle of descent of 0°, and the next dot represents a descent angle of 2.5°.

The angle of descent of an ILS is set by the position of the transmitter equipment on the surface of the airfield. It is something that remains constant, and does not change unless someone on the ground adjusts the actual antennae on the surface of the airfield. The normal position of the ILS antennae are that the Localizer antennae are located at the departure end of the runway, facing the arriving aircraft. The Glideslope antennae are located along side the runway, normally abeam the precision approach aiming point (thousand footers), angled upwards approximately 3°. You can not change this from the aircraft.

Your goal is to keep the Glideslope Indicator centered during your entire descent from the Final Approach Fix. Some pilots will choose to intercept the Glideslope before descending from the Intermediate Fix altitude. In which case, you keep the Glideslope Indicator centered from there. If your indicator is positioned on the dot above center, you are flying below the 3° glideslope. If your indicator is positioned below the center, you are flying below the 3° glideslope.

Always intercept the Localizer before intercepting the glideslope. Beware trying to intercept the glideslope by descending into it from above. Nor should you try to intercept the glideslope before the Intermediate Fix or at an altitude above the Intermediate Fix altitude. You may encounter false signals, otherwise.

One trick to this is to have your aircraft fully configured prior to reaching the Final Approach Fix. This includes:

1. Gear lowered. Prop governor at the highest RPMs. And, flaps set for your descent.
2. Aircraft trimmed for your desired approach speed (preferably the ground speed indicated on your approach chart to time the Missed Approach Point in your aircraft speed category).
3. Power reduced and set to maintain a constant descent vertical speed for a 3° glideslope. This speed may be listed on your chart (depending on whether you use Jepp, NACO, etc.). A good rule of thumb is to multiply your ground speed in knots by 5. This will give you your vertical speed for a 3° descent in feet.
4. Switch on landing, position, and strobe lights. Adjust mixture for maximum power setting. Turn on the boost pump if required by your POH. Fuel selector on the proper tank. And, open carb heat and/or close cowl flaps if so equipped.
5. Stabilize pitch, roll, lateral direction (compensating for wind), power and airspeed (adjusting for half of gust factor).
6. Checklist
7. Start doing all of this 1-2 miles before the Final Approach Fix or when the Glideslope Indicator is a full to a half dot above center. This will give you time to complete everything in time to intercept the 3° glideslope stabilized.
8. Make your Final Approach Fix radio call to ATC or area traffic.
9. Maintain the lateral and vertical guidance ILS center using small, smooth movements of the control yoke. If set properly the first time, you should not have to adjust the throttle until you are preparing to round out for landing or go-around.
10. Keep the ILS centered to within half a dot at all times. If you reach a full dot of vertical guidance, readjust your throttle. If you are at or beyond a full dot at MDA(H) or DA(H), either go-around immediately at the DA(H), or prepare for a go-around at your MAP.