Glideslope callout on take off

[Mike777 163]

4 hours ago, JRBarrett said:

You can taxi onto the threshold of such a runway in any FSX/P3D aircraft equipped with a nav radio and tune the ILS frequency while monitoring the Morse code identifier for the ILS. If you then taxi slowly down to the opposite end of the runway, you will hear the identifier switch as you pass the 50 percent point of the runway’s total length.

 

Been following this thread with much interest!

I took off from Newark (KEWR) Runway 4R last night in the QOT (Drzewiecki scenery).  No glideslope warning at all.  The EWR2 4L/R departure requires initial heading of 039 to 500 ft,a right turn to 60o until I-EZA 4 DME. I-EZA is the 4R ILS designator. 4R and 22L use the same frequency.  I manually set the frequency and course in the NAVRAD ILS block, 108.7/039.  I-EZA does show on the PFD, along with DME, for the first part of the takeoff roll.  But then the PFD display switches to the ID and DME for 22L.  So the DME indication for the departure is not usable.  However, I-EZA shows on the ND as a waypoint (from GPS and INS I presume) so there is no real problem.  But it might be for a less sophisticated aircraft.  I also tried entering 108.7/219 for the ILS frequency but it didn't make any difference. 

I don't know how in the RW aircraft the pilot could force the DME to stay with I-EZA.  Clearly the departure instructions require the 4R DME to be receivable when the transmitter is well behind the departing aircraft, so I am genuinely puzzled.  The instructions also allow I-EWR, the 4L ILS/DME, if I-EZA is not working, but I assume there would be the same problem.  Delta flew DC-9s up until five or six years ago -- they should be able to fly this departure, I think, but how would they deal with the DME?

Mike

 

[downscc 1,327]

3 hours ago, Mike777 said:

I-EZA is the 4R ILS designator. 4R and 22L use the same frequency. 

The DME frequency is linked to the LOC frequency, and if two LOC share the same frequency then in the real world there is one DME transmitter serving both in most cases.  I am aware that at least one British location has two different DME transmitters, and they have to keep one turned off  but that is so typically British.  In the sim world there will be a separate DME for each LOC too, but in all cases I've looked at when two LOC share the same frequency in the US, the two simulated DME are always colocated.  In the FAA database you will see that ILS X and ILS Y share the same DME too.  As a communications engineer, I am pretty sure that you will never have two DME near each other on the same frequency and since their frequency is tied to the LOC (or VOR) the pilot should only be worried that the correct LOC or VOR frequency is dialed in, the corresponding DME should be there.

In the sim world, FSX and P3D always put the DME colocated with the LOC....even if both LOC share the same frequency.  Most payware addon scenery developers don't pay any attention to such things as the DME location so you will see this wrong more times than not.  Just look at the approach plates, they reveal that the DME is probably located with the LOC if the threshold is about 2 DME, or at the GS if the threshold is about 0.2 DME and if the DME at the threshold is about -0.1 DME then it is located at the approach end localizer.  Compare that to what you see in the simulation.... it is often wrong.

[Mike777 163]

9 minutes ago, downscc said:

The DME frequency is linked to the LOC frequency, and if two LOC share the same frequency then in the real world there is one DME transmitter serving both in most cases.  I am aware that at least one British location has two different DME transmitters, and they have to keep one turned off  but that is so typically British.  In the sim world there will be a separate DME for each LOC too, but in all cases I've looked at when two LOC share the same frequency in the US, the two simulated DME are always colocated.  In the FAA database you will see that ILS X and ILS Y share the same DME too.  As a communications engineer, I am pretty sure that you will never have two DME near each other on the same frequency and since their frequency is tied to the LOC (or VOR) the pilot should only be worried that the correct LOC or VOR frequency is dialed in, the corresponding DME should be there.

In the sim world, FSX and P3D always put the DME colocated with the LOC....even if both LOC share the same frequency.  Most payware addon scenery developers don't pay any attention to such things as the DME location so you will see this wrong more times than not.  Just look at the approach plates, they reveal that the DME is probably located with the LOC if the threshold is about 2 DME, or at the GS if the threshold is about 0.2 DME and if the DME at the threshold is about -0.1 DME then it is located at the approach end localizer.  Compare that to what you see in the simulation.... it is often wrong.

Hi Dan,

So if I understand you correctly, my hypothetical Delta DC-9 pilot would not have to worry.  As long as he has the correct frequency (shared by KEWR 22L & 4R) tuned, he will get the correct DME distance for his departure waypoint, regardless of which ILS or LOC beam he is receiving.   But in sim-land, there are two different DMEs for the two different ILS/LOCs.  Indeed I neglected to mention that, when the PFD indication switched to the wrong ILS ID, the DME info changed too, thereby making it useless.  But in fact it was probably wrong even when the correct ILS ID was displaying, due to the wrong location of the DME transmitter.

I suppose it is possible to locate correctly the DME transmitter by having two ILSs with no DME, and then a separate DME at the proper location, all on the same frequency.  I need to check ADE.

Thanks,

Mike

[berts 97]

On 7/23/2018 at 11:02 AM, Qavion2 said:

I believe the key is found in the arming conditions for this mode. The aircraft must descend through 1000ft ra (with the gear down)

The GPWS computer probably monitors the changing altitudes and only arms this mode if the aircraft is seen to be descending through 1000'. Similarly, the altitude callouts need to be armed by the aircraft climbing above a certain height. This prevents nuisance height callouts during climb.

(I don't know if this arming is modelled in QOTSII)

 

Like Dan, I also think Chris's false G/S Warning on takeoff is a Sim based issue and not an inherent fault with the PMDG B744 (E)GPWS; if only because it is not a normal warning for this phase of flight - unless the reciprocal ILS LOC is being used as a departure tracking aid and the crew have forgotten to inhibit the GPWS glideslope warning. 

For a Mode 5 warning "GLIDESLOPE" to be generated it is actually the Landing Gear LEVER that must be down with the aircraft deviating excessively below an ILS glideslope. Pushing the Glideslope Inhibit Switch below 1,000ft Radio Altitude cancels and inhibits the Mode 5 alerts.

A Mode 3 "DON'T SINK" warning is far more likely to occur during a takeoff or Go-around due to altitude loss. This will happen if there is an excessive decrease in barometric altitude during the initial takeoff or go-around and the warning will continue until a positive rate of climb is established ABOVE the original descent altitude when the Mode 3 warning was triggered. 

Given the overall attention to detail PMDG have put into the QOTS and based on my own experience with it, I have little doubt that they have modelled the GPWS system to perform as close to the real aircraft as possible. I managed to get a Windshear warning on a recent approach in heavy rain and what with the cockpit shaking, reduced visibility, noise of the wipers and loud "WINDSHEAR" warnings, the missed approach and go-around felt so realistic I actually broke out in a sweat!

[downscc 1,327]

2 hours ago, Mike777 said:

I suppose it is possible to locate correctly the DME transmitter by having two ILSs with no DME, and then a separate DME at the proper location, all on the same frequency.  I need to check ADE

I have a fair number of payware addons that I have had to use ADE to correct the navaids, it is pretty common.  I think the market is focused on the eye candy and not too many sim pilots pay attention to details like does the DME in the sim world match the charts.

Getting exact lat/lon coordinates for the ILS components used to be a little messy because a very large set of text data files had to be downloaded and then carefully examined to pull out the desired information.  The FAA recently made this much easier by adding an "eBrowser" feature for their National Flight Data Center (NFDC), it is in the list of links midpage here: https://www.faa.gov/air_traffic/flight_info/aeronav/aero_data/

It will only take a few minutes to figure out you are looking for ILS Components.  The LOC antenna, GS antenna and DME antenna locations are given along with other useful information such as beam width, GS angle etc etc.

[Johannvr 3]

6 hours ago, downscc said:

I have a fair number of payware addons that I have had to use ADE to correct the navaids, it is pretty common.  I think the market is focused on the eye candy and not too many sim pilots pay attention to details like does the DME in the sim world match the charts.

Getting exact lat/lon coordinates for the ILS components used to be a little messy because a very large set of text data files had to be downloaded and then carefully examined to pull out the desired information.  The FAA recently made this much easier by adding an "eBrowser" feature for their National Flight Data Center (NFDC), it is in the list of links midpage here: https://www.faa.gov/air_traffic/flight_info/aeronav/aero_data/

It will only take a few minutes to figure out you are looking for ILS Components.  The LOC antenna, GS antenna and DME antenna locations are given along with other useful information such as beam width, GS angle etc etc.

Dan, I think you might be on to something here with the issue with EGCC and the QOTS. I noticed the locations for Manchester's ILS 05L and 23R in Navigraph's Navdata (wpNavAID.txt) are identical. Is this info not used to "program" the FMC when an approach is selected? Where in the NGX you have to enter ILS frequency manually and hence this "false glideslope warning" does not occur with the NGX.

This glideslope warning only happens when departing 23L (which is then closer to 05L glideslope IMM) and not when departing 23R. This can explain why the "Queen" seems to get a bit "confused" with the discrepancy between location data of the ILS's in the AIRAC Navdata and the scenery AFCAD.🙂 The question is, will a corrected Navigraph Navdata solve the problem? We cannot change the Afcad. That will mess up the navaids in relation to the runways of the scenery.

[Johannvr 3]

Just correcting myself and clarification on the AIRAC Navdata. I just learned the locations in the wpNavAID.txt file are the GS transmitter positions as per applicable charts. In EGCC's case, a "shared" GS transmitter I-NN & I-MM 109.50 (CH32Y), positioned at 53.353164, -2.27306 as correctly stated in Navigraph's Navdata file. Looking at EGCC Aerodrome chart, departing 23L positions you in rwy05L's (I-MM) side of the GS transmitter. I think this is the cause of the "confusion" in the QOTS. A mix of accurate simulation in the aircraft nav systems and flightsim shortcomings in scenery afcad files.

The solution is, I think, we recognize this as a sim issue and just ignore the "glideslope" warning. It's just another voice in the cockpit talking to you and you don't have to feel so alone.😁

Edited July 25, 2018 by Johannvr

[Qavion2 39]

21 hours ago, JRBarrett said:

o during the climb phase after takeoff, there is no way to avoid passing through the glideslope beam for the opposite end of the runway, penetrating it from above, then ending up below unless the climb angle is quite steep.

My books specify a front course. This surely means the GPWS is just as smart as the PFD displays. The GS needle won't show on the PFD for intercept angles greater than 90 degrees to the front course.

 

21 hours ago, JRBarrett said:

The signal level reaching the glideslope antenna from behind the aircraft would be less than optimal, but might still be sufficient to give an indication, especially when still close to the transmitter.

The indications will probably be so erratic after passing the transmitter (relying on reflections from ground objects), it wouldn't generate a warning. How many cockpit landings can you find on YouTube where the G/S pointer remains in view past, say, the mid point of the runway?

Engineering 747-400 manual quote:

Mode 5 is armed when the airplane descends below 1000 feet RA,
the landing gear is down and the localizer is captured (within 2 dots)
before descending below 500 ft.

To rearm mode 5, the airplane must either descend
below 30 ft RA or ascend above 1000 ft RA.

 

Heading Compare
The backcourse compare circuit inhibits mode 5 annunciations
during backcourse. The airplane is in backcourse when the angle
between selected runway heading and magnetic track is greater
than 90 degrees.

Edited July 25, 2018 by Qavion2

[JRBarrett 3,034]

3 hours ago, Qavion2 said:

My books specify a front course. This surely means the GPWS is just as smart as the PFD displays. The GS needle won't show on the PFD for intercept angles greater than 90 degrees to the front course.

 

The indications will probably be so erratic after passing the transmitter (relying on reflections from ground objects), it wouldn't generate a warning. How many cockpit landings can you find on YouTube where the G/S pointer remains in view past, say, the mid point of the runway?

I’m sure that structural signal blocking in an aircraft the size of a 747 would be significant. It would probably be far less on a small GA aircraft like a C172, that might be using the tail-mounted VOR antenna to also receive glideslope signals via a splitter. But, I don’t think many Cessna recips are equipped with EGPWS!

Of course, antenna reception patterns aren’t really modeled in a sim like FSX/P3D.

It’s still somewhat puzzling why this spurious EGPWS glideslope warning on takeoff seems to only occur consistently with the PMDG 744 at Manchester, since there are many other airports in the sim world that use a common ILS frequency for both ends of a given runway. 

[Christopher Low 5,332]

On a side note (and since Dan mentioned it).....I notice that some airport runways have "ILS Y" and "ILS Z" options. What exactly is the difference between them?

[JRBarrett 3,034]

50 minutes ago, Christopher Low said:

On a side note (and since Dan mentioned it).....I notice that some airport runways have "ILS Y" and "ILS Z" options. What exactly is the difference between them?

When there are multiple ILS approach plates to a given runway with letter suffixes like “Z” or “Y”, the “Z” approach will be the one with the lowest minimums. The “Y” approach will have higher minimums, and if there is an “X” approach, it will have higher minimums still.

The difference is in the onboard equipment the aircraft is required to have to fly a given approach. The “Z” approach might require an RNAV-certified GPS and/or DME in addition to an ILS receiver, while the “Y” approach might only require the ILS receiver.

[Mike777 163]

Regarding the aircraft's fuselage blocking signals coming from behind (RW): It seems to me that at least the DME signals must be received reliably, or else departures using an ILS's DME as a waypoint would not be possible -- such as several at KEWR.

Mike

Edited July 25, 2018 by Mike777

[JRBarrett 3,034]

6 minutes ago, Mike777 said:

Regarding the aircraft's fuselage blocking signals coming from behind (RW): It seems to me that at least the DME signals must be received reliably, or else departures using an ILS's DME as a waypoint would not be possible -- such as several at KEWR.

Mike

The DME antennas on an aircraft are normally located on the lower fuselage, and have an omnidirectional reception pattern. Also, the antenna of a DME transmitter radiates equally in all directions.

The glideslope antenna on a transport-category aircraft is typically located inside the nose radome, and is designed to only receive signals coming from in front of the aircraft, and the ground-based glideslope antenna is highly directional as well.

[Mike777 163]

9 minutes ago, JRBarrett said:

The DME antennas on an aircraft are normally located on the lower fuselage, and have an omnidirectional reception pattern. Also, the antenna of a DME transmitter radiates equally in all directions.

The glideslope antenna on a transport-category aircraft is typically located inside the nose radome, and is designed to only receive signals coming from in front of the aircraft, and the ground-based glideslope antenna is highly directional as well.

Thanks!  I thought their might be a difference between ILS/LOC receivers and DME receivers.

Mike

[Qavion2 39]

7 hours ago, JRBarrett said:

The DME antennas on an aircraft are normally located on the lower fuselage, and have an omnidirectional reception pattern.

Since they are forward of the main landing gear, it's probably best to have your gear up to prevent interference. I'm wondering if the original poster still had his langing gear lever down when he got the glideslope alert? As far as I can see, there should be no alert with the gear lever up (or off).

 

7 hours ago, Mike777 said:

Regarding the aircraft's fuselage blocking signals coming from behind (RW): It seems to me that at least the DME signals must be received reliably, or else departures using an ILS's DME as a waypoint would not be possible -- such as several at KEWR.

The DME component of the glideslope ground transmitter is probably omnidirectional (as well as the receiving antennae). Caution must be used when using ILS-DME. DME transmissions contain an electronic offset to compensate for different ground antenna locations (with respect to the runway threshold). i.e. the transmitter may alter the response time delay to compensate for the antenna location. Depending on the relative position of the aircraft in relation to the antenna, you may get a substantial distance error.