Glide slope capture

[mdeval]

Thoroughly enjoying the L-1011 I recently downloaded and installed. Tried my first autopilot coupled ILS approach. All went well, the AP grabbed the localizer but at the GS intercept point, the plane kept on straight and level. Had to disconnet the AP to land manually. Airspeed at the capture point was 170 kts, flaps about half as I recall. I really don't feel as if I had too much speed.

Anyone know what went wrong ?

Mike

[aerofoto - HJG Admin]

A fundamental fact/reality is that flying AP controlled ILS coupled auto-approaches to landing within FS is often not absolutely perfect ....

Some simulations differ in their ability to fly such approaches well .... and so do the results of ILS approaches associated with some FS airport RWY's too .... from my extensive pre-release testing experience.

Thi's my own basic advice when flying AP controlled ILS coupled auto-approaches to landing ....

- Ensure your simulation isn't overweight .... in fact one shouldn't, be attempting landing with more than 20-25% total fuel remaining .... on top of a full payload.

- Not too high .... flying a 20 DME circuit/pattern around any FS airport at no more than 5000 FT is perfectly adequate. The maximum FS distance for any ILS intercept is roughly 20-25 DME from the RWY threshold. In FS .... and from my own personal experience .... the longer the ILS auto-approach to landing then the better/more precise the result.

- Not too fast .... ILS intercepts shouldn't be performed in excess of 180 KIAS .... and should then be progressively reduced to around 155-145 KIAS during the approach to landing. Speed will vary according to aircraft type, flap/gear extension limitations, and distance to run. For the L1011 and DC10 (with 20% total remaining fuel) I vary speed .... as I feel is necessary .... between 150-145 KIAS .... whilst also trying to retain a nose-up pitch attitude (AI) of roughly 3-4* (degrees) for either of these 2 aircraft types only. During AP controlled ILS coupled auto-approaches to landing any simulation may be observed to gently/slowly rise and descend .... in fractions of increments .... as the RWY is neared .... and from around 10 DME in particular. In such cases my own practice is to reduce speed, by a few KTS, whenever pitch is observed to decrease slightly .... and .... increase speed, by a few KTS, whenever pitch is observed to increase slightly .... I find this usually results/assists in a "very stable" approach. One's also got to be careful here too .... because insufficient speed will always result in the nose pitch attitude drifting "UP" .... to the point of even possibly obscuring RWY visibility and/or inducing a stall .... whereas excessive speed will always result in the nose pitch attitude drifting "DOWN". Speed/Power, weight, and pitch attitude are critical. These sorts of approaches, in FS, can only really be perfected by lots of "practice and familiarity" with one's simulation of choice.

- Not too acute an angle of intercept is also another very good rule of thumb. Normal ILS intercepts shouldn't be performed at angles exceeding than 20-25* (degrees) of the RWY centerline. Having said this though .... my L1011's and DC10's have no problem .... WHATSOEVER .... flying even 90* (degree/right angle) ILS intercepts and then mainting the GS/RWY centerline throughout the approach to landing too .... provided that altitude (5000 FT), speed (200-180 KTS), and distance (20 DME) in are "all" in my favor .... as well as through careful monitoring/adjusting of speed and power, and then flap and gear extension during the approach to landing. What one will most likely observe in FS .... and this is certainly the case with most aircraft (including the L1011 and DC10 .... is that within the last 1000 FT and/or 1-2 DME from the RWY threshold .... the simulation may begin to loose the GS .... triggering "pregnant dogging Betty to start screaming" ;D This sort of situation varies from FS aircraft to FS aircraft type/FDE and there's really no perfect solution .... other than to disconnect the AP and AT, early, at around 800-500 FT .... be ready to address power and trim if necessary .... and then continue the approach to landing/touchdown "MANUALLY".

Most FS aircraft can probably handle a "COMPLETELY AUTOMATIC ILS COUPLED AUTO-APPROACH ALL THE WAY DOWN TO LANDING/TOUCHDOWN .... but .... such landings will often be quite firm and may, on occasion, even result in a "CRASH"

Flying a straight-in ILS approach to landing within FS can/does often result in the simulation completely missing the intercept .... from my own personal experience. A downwind .... followed by base legue pattern (the latter legue during which "APPR" is activated early) generally always results in the bests approaches to landing.

That's the best advice I can provide for you .... and .... that's FS for you too. A bit different from he realworld i'm afraid .... BUT .... I hope this will assist you anyway !

See how you go, but, you should know that are "no problems/issues" in regard to AP controlled ILS coupled auto-approaches to landing (othan than what's hilited above) with any of our L1011's !

Mark

[walterleo]

Hi Marc:
Only to add, that as in real flying: Never try to intercept the glideslope from above. This does not happen if one flies as you described it below 5000 ft QFE 25 miles out. But often one tries to capture GS from above in FS, cause you dont have a flightinstructor or captain sitting beside you and crying NO NO NO IT could be dangerous!!! ;D

Walter

[Dan K. Hansen]

Did you set your AP to NAV1 pretty vital to actually catch the GS ....

[jimhalinda]

Another possibility, which happens to me a lot. Were you in GPS mode perhaps? I often forget I'm in GPS mode and start an auto approach, forgetting to change over to use the NAV1 and Localizer. The plane seems to start the approach OK, but obviously doesn't behave the way I expect it to!

Regards,

Jim

[aerofoto - HJG Admin]

From what I've seen myself .... and as I implied above ....

ILS intercepts within FS can be temperamental when flying a straight-in approach .... more-or-less directly at the RWY centerline. 5 times out of 10 times the simulation can miss the intercept completly.

This can happen also if trying to fly an ILS intercept too close to any RWY threshold .... or .... a bad intercept can result through the simulation then having less time/distance to stabilize on the ILS/GS.

As I mentioned earlier .... flying a downwind legue, followed by a base legue during which the ILS is first captured, is, from my own personal experience, by far the best way to fly an AP controlled ILS coupled auto-approache to landing in FS .... 9.5 times out of 10 times no problems at all will result .... BUT .... the similation/approach still needs to be monitored, quite closely, all the way down to the RWY.

Definitely .... the longer the approach .... under 25 DME .... then the better/more stable ILS approache seems to become in FS .... provided distance and altitude are in ones favor to start with, and then power/speed, and attitude are all properly monitored, and adjusted, where necessary throughout the approach to landing.

Some folk might think one should be able to lock on to an ILS/GS .... and then leave the simulation to fly itself merrily all the way down to the RWY .... but unfortunately .... it doen't work like that .... not even in FS !

Mark C
AKL/NZ

[mdeval]

So I've not had this problem since writing the last time. Don't know what I'm doing differently but the AP captures the glide slope every time.

The next question though is this: Doesn't seem that I can get the rate of descent to any more than 700-800 fpm while the airspeed hold is on and at 230-240 kts. If I disengage the airspeed hold and reduce thottle to almost idle, I can get 1500-2000 fpm which seems to be a more correct rate and the airspeed remains within workable (220-240) limits. Which method is correct ?

Mike

[aerofoto - HJG Admin]

There is a peculiarity in the L1011 panels AP.

It's not that there's anything wrong with it .... because there's nothing wrong with it at all .... BUT RATHER .... it just has to be used differently because of the peculiarity which exists within its engineering/the way it's been designed.

Allow me to start explaining by saying .... prior to engaging the L1011 AP you should first have dialed-up both target altitude and and specific ROC values .... THEN engage the AP .... AND THEN engage the ALT tab. Using the AP function you should then be able to adjusst your ROC/ROD as desired.

The AT works completly independently of the AP. It's a simple matter of setting a target speed value .... THEN activating the AT tab. There's really no relationship between this AT or AP controlled ROC/ROD functions in these L1011 panels for normal/prescribed operations.

Getting back to the AP .... and it's ROD function "IN PARTICULAR" .... because, as I mentioned above, there "IS" a peculiarity associated with setting the ROD due to the design/engineering of this AP.

The best way oo initiate and control ROD using this AP is as follows ....

1. Disconnect the ALT HLD tab ("DO NOT" disconnevt the AP though)

2. Select a target altitide

3. Select a 100-200 FPM ROD

4. Re-engage ALT HLD .... and then reselect a better ROD .... up to around 2500 FPM .... and then adjusting this appropriately as you descend.

"THIS" is simply the way in which "THIS" particular AP has been designed/engineered to work and there's nothing we/HJG can do to change it .... short of implimenting a completely new/different AP system into each of these L1011 panels.

Here's an extract from my online/forum manual for our L1011 aircraft .... in particular the section of this manual relating to "descent" using both the AP and AT systems ....

1.6 DESCENT
==============

From a cruising altitude of 31,000 FT the descent is best commenced at approximately 100 miles DME from any destination airport. The ROD and airspeed must be closely monitored in relation to the DME indications, and adjusted if necessary, in order to arrive at 10,000 FT by approximately 30 miles DME from any destination airport .... and at a sensible airspeed.
By far the best manner to decend these L1011 aircraft is as follows :-

Upon reaching the TOD point the AP "ALT HLD" switch should be temporarily disengaged (do not disengage the AP). The Altitude Selector should then being reset to a new target altitude value .... approximately 17,500 FT (roughly transition altitude). The Vert Speed thumb wheel should first be set at an intial and very slow 200 FPM ROD. The "ALT HLD" switch should then be re-engaged .... and the Vert Speed thumb wheel then reset for an approximately 2000 FPM ROD. This slightly abnormal AP procedure ensures smooth transition from level cruise to descent and aids avoiding sudden and unauthentic pitch changes that can be induced by the AP when descent is commanded during automatic flight control mode.

When flying in controlled IAS/MACH speed modes the AT system will automatically reduce engine thrust when descent is commenced. Airspeed during descent will still need to be monitored and adjusted, if necessary, to ovoid overspeeding the aircraft.

Descending through 27,000 FT to 25,000 FT the AT "MACH HLD" airspeed control function should be disengaged. A target "IAS" airspeed of approximately 270 KIAS to 290 KIAS (depending on aircraft version) should then be selected and the AT "IAS SPD HLD" function then engaged. Again the ROD must be carefully monitored, and adjusted throughout the remainder of the descent and in relation to both airspeed and distance from any destination airport. If the airspeed increases too much .... then the ROD should be reduced. If the airspeed reduces too much, then the ROD may be further increased, or, engine power increased as necessary in order to acquire a sensible speed.

Here a link to my "FULL/COMPLETE" online/forum manual for the L1011's and their panels ....

L1011 TRISTAR Panel Installation & Handling Notes
tonymadgehjg.proboards.com/index.cgi?board=supportpage&action=display&thread=3888

These notes go a long way beyond providing just panel installation advice .... to describe most of what's essential to be understood in order to be able to enjoy these simulations to the maximum. "SECTION 1" of these service notes describes our L1011 project in detail .... including known issues. "SECTUION 2" of these service notes explains how these L1011 panels should be set up/used/flown for best performance. "SECTION 3" of these service notes feature "BASIC FLYING GUIDES" for each of the L1011 versions we represent. Each of these aircraft are different by virtue of their weight and/or engine thrust (or both) .... therefore the performances of each of these aircraft varies accordingly too.

I think you'll find this information quite valuable .... "IF" you're new to our L1011 simulations.

Mark C
AKL/NZ