Autopilot and ILS crashes 747

[Sammy Yousef]

Hi,

I'm relatively new to FS2004, and I'm just trying to learn to land the
747 using ILS and autopilot.

I've set up a flight where I'm just about to capture the glide path at
2000ft at Sydney airport. I have no problem capturing the glide path.
Alt switches off on the autopilot when I intercept. However the
autopilot was crashing the 747 on landing. It was bobbing the aircraft
up and down slightly, which I believe was causing the problem. I started
speeds from 140 knots to 200 in increments of 10. 140 falls out of the
sky. 170 crashes, 150 is perfect (no crash).

Is this a bug or am I missing something vital? Does a real ILS behave
this way? Is there an easier way to determine the correct speed?

Forgive my ignorance if I'm missing something obvious

Thanks,

Sammy

[S Herman]

On Tue, 05 Jul 2005 14:09:44 GMT, Sammy Yousef
> wrote:


>speeds from 140 knots to 200 in increments of 10. 140 falls out of the
>sky. 170 crashes, 150 is perfect (no crash).
>
>Is this a bug or am I missing something vital? Does a real ILS behave
>this way? Is there an easier way to determine the correct speed?
>
>Forgive my ignorance if I'm missing something obvious
>
>Thanks,
>
>Sammy

Yes approach speed is critical. The key to a good landing is a
stabilized approach. Being stabilized farther out makes it easier.
Make sure the flaps are set correctly for each airspeed change. Also,
you may want turn off the autopilot at 100-200 ft AGL, and flare the
plane manually. Most real airliners are not flown to the ground on AP.
170 is too fast and you are hammering it into the ground. 140 is
probably stalling, that's the bobbing.

[Sammy Yousef]

Hi again.

Thanks for the reply.

I actually stall and fall out of the sky at 140, but bob at 170 and
above. Which is what I don't understand. I can understand hitting too
hard but why can't I get stable at a higher speed? Is it because I have
flaps set at this speed that the autopilot can't hold a straight
approach to the runway?

I have no problems at all if I turn off the autopilot and flare
manually, even at 170 and above.

Thanks again,

Sammy

S Herman wrote:
> On Tue, 05 Jul 2005 14:09:44 GMT, Sammy Yousef
> > wrote:
>
>
>
>>speeds from 140 knots to 200 in increments of 10. 140 falls out of the
>>sky. 170 crashes, 150 is perfect (no crash).
>>
>>Is this a bug or am I missing something vital? Does a real ILS behave
>>this way? Is there an easier way to determine the correct speed?
>>
>>Forgive my ignorance if I'm missing something obvious
>>
>>Thanks,
>>
>>Sammy
>
>
> Yes approach speed is critical. The key to a good landing is a
> stabilized approach. Being stabilized farther out makes it easier.
> Make sure the flaps are set correctly for each airspeed change. Also,
> you may want turn off the autopilot at 100-200 ft AGL, and flare the
> plane manually. Most real airliners are not flown to the ground on AP.
> 170 is too fast and you are hammering it into the ground. 140 is
> probably stalling, that's the bobbing.

[S Herman]

On Tue, 05 Jul 2005 20:53:29 GMT, Sammy Yousef
> wrote:

>Hi again.
>
>Thanks for the reply.
>
>I actually stall and fall out of the sky at 140, but bob at 170 and
>above. Which is what I don't understand. I can understand hitting too
>hard but why can't I get stable at a higher speed? Is it because I have
>flaps set at this speed that the autopilot can't hold a straight
>approach to the runway?
>
>I have no problems at all if I turn off the autopilot and flare
>manually, even at 170 and above.
>
>Thanks again,
>
>Sammy

It's the nose bobbing up & down? Is it only the 747? You may be able
to change the .cfg file.

Find the recommended IAS for the various flap/gear settings & stick to
them.

If the pitch & power are set with any given flap & gear
configuration, the plane should seek out and hold a stable airspeed,
whether climb, level or descent. Now whether this matches the
GlideSlope is another thing.
If you are too fast, the AP may chase the glideslope, so it pitches
down to get lower, penetrates the GS low, then reverses pitch to climb
back up to the GS, a vicious cycle.. This happens to human pilots too,
pilot induced oscillation, or "porpoising" is one common error.

[Paul Riley]

"S Herman" > wrote in message
...
> On Tue, 05 Jul 2005 20:53:29 GMT, Sammy Yousef
> > wrote:
>
>>Hi again.
>>
>>Thanks for the reply.
>>
>>I actually stall and fall out of the sky at 140, but bob at 170 and
>>above. Which is what I don't understand. I can understand hitting too
>>hard but why can't I get stable at a higher speed? Is it because I have
>>flaps set at this speed that the autopilot can't hold a straight
>>approach to the runway?
>>
>>I have no problems at all if I turn off the autopilot and flare
>>manually, even at 170 and above.
>>
>>Thanks again,
>>
>>Sammy
>
> It's the nose bobbing up & down? Is it only the 747? You may be able
> to change the .cfg file.
>
> Find the recommended IAS for the various flap/gear settings & stick to
> them.
>
> If the pitch & power are set with any given flap & gear
> configuration, the plane should seek out and hold a stable airspeed,
> whether climb, level or descent. Now whether this matches the
> GlideSlope is another thing.
> If you are too fast, the AP may chase the glideslope, so it pitches
> down to get lower, penetrates the GS low, then reverses pitch to climb
> back up to the GS, a vicious cycle.. This happens to human pilots too,
> pilot induced oscillation, or "porpoising" is one common error.

Also make sure you are not too heavy. Your fuel should be around 25%. For
sure less than 40%. That may help. What does the flight notes for that
aircraft say. I don't fly heavies--too much like being a bus driver :-)

Paul

[R.V. Gronoff]

Sammy Yousef a écrit :
> Hi,
>
> I'm relatively new to FS2004, and I'm just trying to learn to land the
> 747 using ILS and autopilot.
>
> I've set up a flight where I'm just about to capture the glide path at
> 2000ft at Sydney airport. I have no problem capturing the glide path.
> Alt switches off on the autopilot when I intercept. However the
> autopilot was crashing the 747 on landing. It was bobbing the aircraft
> up and down slightly, which I believe was causing the problem. I started
> speeds from 140 knots to 200 in increments of 10. 140 falls out of the
> sky. 170 crashes, 150 is perfect (no crash).
>
> Is this a bug or am I missing something vital? Does a real ILS behave
> this way? Is there an easier way to determine the correct speed?
>

Nope, jumbos land at 150kt. In case you're a bit too high on the slope,
add 10-20kt then slow back to 150 when you're at the right alt.

Just for your knowledge: normal twin jets commercial planes (b737,
a320...) land at 135kt and private jets at 125-130.


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