PSX Inertial Landing.

[Mariano]

Hardy,

Not an important request, but a nice feature to add when you have some time, say... sometime around fourth quarter 2017.

Will we be able to program a LOC or GS signal failure below AH (or at a very low height) so as to be able to simulate an inertial landing?

I wouldn't be surprised if you have already added this function (with corresponding extra crisp screenshots to follow.)

Thanks,

Mariano

[Jeroen Hoppenbrouwers]

As far as I know, the last parts of the landing are always done on inertial only anyway. So I don't know what would be different when the ILS guidance fails at that moment. Certainly no wild movements or Christmas lights on the panels. Any idea?

Rollout -- definitely a different story!


Jeroen

[John H Watson]

The Autoland system needs more than just inertial guidance. It needs Radio Altimeter height for the flare. Otherwise it will just hit the runway at 700'/min

The IRS has no idea how high you are above the runway.

Rgds
JHW

[Jeroen Hoppenbrouwers]

Sure, I just meant "no LOC or GS" -- thanks for the completion.

[Blake H]

GS above 200 ft for guidance, below 200 ft guidance transits to radio alt decent at 20fps. Rollout

GS gets to sensitive for navigating and possible errors as the aircraft approaches the GS transmitter.

I am talk rough numbers. From a pilot training manual for AUTOLAND

LOC is always required for guidance unless you plan to go off the runway. Believe the 744 has 3 channels plenty of redundancy. IRS are just for attitude on the ILS not navigation not guidance.

Radio alt is the big player is decides when events (modes) will occur.

Blake.

[Mariano]

Hi guys,

From what I've read, if you loose LOC signal below, let's say, 80FT AGL, the IRSs (or FCCs, I don't really know) will "remember" the wind correction angle, and will hold that (hoping to continue to track the runway center line) until touchdown. Without a LOC signal, the only obvious candidate to continue the lateral part of the approach are the IRSs (via the FCCs.)

I was wondering if we'll be able to program a very low height LOC signal failure to be able to continue a CAT III approach in PSX.

Thanks,

Mariano

[John H Watson]

GS above 200 ft for guidance, below 200 ft guidance transits to radio alt decent at 20fps.

If anyone is alive after that landing, I'd be quite surprised :mrgreen: In reality, a 12 or so fps descent followed by a flare which aims at 1.5fps at touchdown is more realistic (as well as comfortable).

GS gets to(sic) sensitive for navigating and possible errors as the aircraft approaches the GS transmitter.

As the aircraft approaches the transmitter, signal processing allows for this sensitivity.

I am talk(sic) rough numbers. From a pilot training manual for AUTOLAND

Rough numbers in this case equate to a rather rough landing

IRS are just for attitude on the ILS not navigation not guidance.

The 744 Autoland system has inertial assistance. This enables the aircraft to
follow the ILS even if ILS signals are lost for a short period, or significantly deflected by passing traffic (for a short time).

Rgds
JHW

[farrokh747]

hello - where are the gs, loc and ra antennae located on the 744? are there more than one for each?

[John H Watson]

hello - where are the gs, loc and ra antennae located on the 744? are there more than one for each?

No more than two for each system  

Each RA system has a transmit and receive antenna (underneath the fuselage) at a previously mentioned "station 900" (Longitudinal Boeing 747-400 station numbers can be equated to "inches from the nose minus 90").

The G/S and Loc antennae have "capture" and "track" variations. With the landing gear retracted, the G/S systems use capture antennae mounted behind the radome. With the landing gear down, the G/S systems use track antennae mounted on the front of the nosegear doors (small, aft ones). Prior to pushing the APProach button on the MCP, the Loc systems use the VOR tailfin antennae. After selecting APProach, track antennae mounted behind the radome are used.
The switch in antenna location allows for better tracking and less signal interference from parts of the fuselage (when the aircraft is in a nose up attitude).

Rgds
JHW.

[farrokh747]

thanks john - so is there a built in bias to account for the cable run from the ra antenna to the box in the avionics bay? i'm thinking at say, 30 ft, the cable run would be longer than the ht of the antenna from the ground...  has this anything to do with the ra on ground showing -8? i've always wondered what exactly the callout height is from - the rear tyre of the body gear? or is it approximated to a given point....

fc

[Jeroen Hoppenbrouwers]

RA is calibrated to read zero at first tire touchdown when the aircraft is in a normal flare attitude at normal landing weight.

Most systems that use signal travel time to measure distance have some built-in correction factor. This also is true for DME equipment: there are installations that read 0 at 2 nm distance, so they read -2 at the station. This all is done by having the electronics always  biased, so that corrections can be made both by a delay increase and a delay decrease below readout zero.

Essentially, all these units are manufactured to read -10 when receiving 0 so to say, and cables or delays are added to read zero after installation. A bit like mechanical stuff allows for tolerances to be pushed out by a screw.


Jeroen

[Blake H]

Even if the signal is lost for a 1 sec still needs LOC signal. Maybe not GS you have a self contained rad alt on board.

My aircraft Radio alt read 0 on the ground you would think that they try to place the antenna for the rad alt as close below the centre of gravity. This is where you would get least amout of error. (pitching and banking)

Turning more then 5 degrees bank really throws the numbers out. You could be lower then what you are if you are banking and using the rad as a refer height. Scared me a few times, low cloud circling approaches to a aerodrome with no aids. You naturally start searching for situation information. Don't chose the wrong one. Know you aircraft limitation.   :shock:

[Jeroen Hoppenbrouwers]

RA is designed to provide accurate vertical height info only for stable, straight-in approaches, and ILS autoland also needs a level ground segment a few hundred meters before the runway threshold. It isn't a good replacement for barometric altitude.

Terrain following radar is quite a bit more complex than RA... as you say, know the limitations!


Jeroen

[John H Watson]

Even if the signal is lost for a 1 sec still needs LOC signal. Maybe not GS you have a self contained rad alt on board.

I don't have the values handy for the 747-400, but on a similar aircraft, the B767, depending on Flight Control Computer options, the autopilot tolerates the loss of G/S signal for up to 15 seconds and the loss of LOC is tolerated for 20 seconds. Below 200', however, the loss is only tolerated for 4 seconds. The autopilot is quite happy to follow IRU ground track, etc, until the signal is re-established.

Turning more then 5 degrees bank really throws the numbers out.

The 744 Rad Alt system is designed to give accurate readings with reasonable bank angles. The radiation pattern is not a pencil beam, but a cone. The signals which return to the aircraft in the least amount of time are used to make height computations.

so is there a built in bias to account for the cable run from the ra antenna to the box in the avionics bay?

Correct. A bias is applied as required for the particular installation. The Rad Altimeter Transceivers are fitted in the Centre Equipment Centre (not the Main Equipment Centre), to minimise the bias. Cable length is ultra critical (e.g. I believe if you cut 1/4" too much off the coaxial cable during installation, you have to throw the cable out and start again).

[Hardy Heinlin]

Mariano,

how exciting is that malfunction? The ILS indications may disappear and after some seconds reappear, while the A/P keeps riding the virtual beam. That's all.

Or am I missing something special?


Cheers,

|-|ardy

[Mariano]

Hardy,

Not a particularly exciting one (unless on the real thing ;-) Landing in almost zero visibility having lost the LOC signal just below AH must be lead to a few 'tense' seconds, I imagine, especially during rollout with a crosswind.

As I said not a big one, just interesting.

Thanks,

Mariano

[Hardy Heinlin]

OK, I'll try.


(Of course, one could depower all three ILS receivers, but that would be a rare coincidence. So it must be the ground transmitter that fails.)

[the mad hatter]

Mr Hardy,

It does happen in real life where the ILS disappears altogether, it happened to me in Africa a number of years ago... the buggers cut the wires and everything else they cut cut and ran off with them in a white Hi ace van... I was later told that they often take wiring and melt it down for cash! Needless to say the "Office" was quite entertaining at the time, T'was no big deal
 
this has happened at Lanseria a couple of times and Capetown

[Jeroen Hoppenbrouwers]

... today in the Netherlands, two major rail disruptions again, due to buggers cutting and dragging away a few hundred meters of copper wire used for the signalling system ... happens daily since a few years  :-(


Jeroen

[Hardy Heinlin]

Will we be able to program a LOC or GS signal failure below AH (or at a very low height) so as to be able to simulate an inertial landing?

Yes.


|-|