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#1
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Unusual Honeywell KLN94 aviation GPS failure - what could causethis?
I have seen that indication when the antenna did not have a clear view
of the sky. The installed aircraft was an EADS/Socata TB-9 with gull wing doors. Coming out of the pad, the pilot's door when up (as it was in the summer) would obscure much of the sky and not allow the GPS to get a position. Resolved by removing the blockage by repositioning the plane or lowering the door. The antenna in this case was on the roof of the cabin between the two gull-wing-doors. Peter wrote: http://www.peter2000.co.uk/aviation/kln94-failure/ This unit has been working perfectly for four years, and works fine now. Peter. -- Return address is invalid to help stop junk mail. E-mail replies to but remove the X and the Y. |
#2
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Unusual Honeywell KLN94 aviation GPS failure - what could causethis?
Ooops. Only looked at pic number 1, not the ones showing the sat
reception. Only time I've had a slow position computation is when the unit has been powered down for a LONG (weeks to months) time. Takes up to 15 mins for it to "find itself" while remaining still. An intermittent connection on the internal battery (there is a small watch battery on the board inside - at least the KLN-89/B does) to keep last known position and user waypoints stored. You didn't have any error/hardware error messages on startup? Dave Dave S wrote: I have seen that indication when the antenna did not have a clear view of the sky. The installed aircraft was an EADS/Socata TB-9 with gull wing doors. Coming out of the pad, the pilot's door when up (as it was in the summer) would obscure much of the sky and not allow the GPS to get a position. Resolved by removing the blockage by repositioning the plane or lowering the door. The antenna in this case was on the roof of the cabin between the two gull-wing-doors. Peter wrote: http://www.peter2000.co.uk/aviation/kln94-failure/ This unit has been working perfectly for four years, and works fine now. Peter. -- Return address is invalid to help stop junk mail. E-mail replies to but remove the X and the Y. |
#3
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Unusual Honeywell KLN94 aviation GPS failure - what could causethis?
How long were you in a static position on the ground? Less than 15 mins
or more than 15 mins? For whatever reason, if the box has "lost itself" with regards to its last known position, or if the box is powered up more than 50 or so miles away from its last known position, it can take "a while" to find itself, and my understanding is that you need to be still while this is happening. This process can be accelerated by entering your current position into the box on one of the menu screens. I've got two 89 series GPS's on my workbench, one of which will be used for an upcoming experimental installation. My only references into this matter are dealing with those two boxes, and the installation manual for the 89 series. You say the problem is fixed now, as in, not recurred? Do you have any user defined waypoints? If there are/were, and are not now, this might point to a problem in the memory (powered by that little battery).. maybe there is an intermittent break in the power supply. You indicated the box was opened within the past few months - could be pertinent in troubleshooting this item. Good luck, Dave Peter wrote: There were no errors showing on the KLN94, other than the lack of a fix. I think this failure is unusual because - as far as I can tell - the SV (space vehicle) signal indications are all normal, but the GPS isn't producing a fix (STATE NAV D). It is as if there was a disconnection between the GPS receiver and the rest of the unit - all this is internal to the KLN94 so ARINC buses don't come into it; the KLN94 doesn't have an ARINC bus anyway, and the KMD550 MFD doesn't use ARINC, it gets the data via RS232. It took an hour to get a fix, which is too long for any kind of slow acquisition. The previous time it was on was about 2 days earlier; a 5 hour flight. If the problem was just showing on the KMD550 then one could understand a bad connection, but this is entirely internal to the KLN94. Satellite geometry can't be the issue because the two other GPSs (one of which was using the same type of rooftop antenna as the KLN94) were receiving fine. The internal KLN94 battery should not be relevant once the power is on. It was also changed a few months ago. Presently I have no idea what this could be. I believe the KLN94 contains a separate GPS receiver module which emits an NMEA stream to the rest of the unit. This stream is in fact accessible via a connector pin on the back of the unit. A break in this stream would account for this issue - but how does the main processor get the SV reception data? I thought that stuff comes down the same NMEA data stream, which is how (nearly) every GPS on the market is able to display the constellation details. I even changed the DME frequencies, while still on the ground, in case it was a DME harmonic messing with the GPS signal (that's a well known one). However, I may not have done that for long enough. The trouble with that theory is that such interference should show up in the SV signals too. The selected VOR/DME would have been 113.4 MHz. I don't know if that is a harmonic of the GPS signal. Also the failure persisted for about an hour, by which time I would have long been tracking a different VOR. Dave S wrote Ooops. Only looked at pic number 1, not the ones showing the sat reception. Only time I've had a slow position computation is when the unit has been powered down for a LONG (weeks to months) time. Takes up to 15 mins for it to "find itself" while remaining still. An intermittent connection on the internal battery (there is a small watch battery on the board inside - at least the KLN-89/B does) to keep last known position and user waypoints stored. You didn't have any error/hardware error messages on startup? Dave Dave S wrote: I have seen that indication when the antenna did not have a clear view of the sky. The installed aircraft was an EADS/Socata TB-9 with gull wing doors. Coming out of the pad, the pilot's door when up (as it was in the summer) would obscure much of the sky and not allow the GPS to get a position. Resolved by removing the blockage by repositioning the plane or lowering the door. The antenna in this case was on the roof of the cabin between the two gull-wing-doors. Peter wrote: http://www.peter2000.co.uk/aviation/kln94-failure/ This unit has been working perfectly for four years, and works fine now. Peter. -- Return address is invalid to help stop junk mail. E-mail replies to but remove the X and the Y. |
#4
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Unusual Honeywell KLN94 aviation GPS failure - what could causethis?
On 09/11/06 13:54, Peter wrote:
Dave S wrote How long were you in a static position on the ground? Less than 15 mins or more than 15 mins? In a static position, maybe 5 mins. Then another 10 mins before getting airborne. The issue is that *if* the box lost it's position (for whatever reason), that unless it's sitting still for up to 15 minutes, it may take it quite a while to determine it's position (I presume this is due to problems it has in determining it's position while it's moving). For whatever reason, if the box has "lost itself" with regards to its last known position, or if the box is powered up more than 50 or so miles away from its last known position, it can take "a while" to find itself, and my understanding is that you need to be still while this is happening. This process can be accelerated by entering your current position into the box on one of the menu screens. The thing is that I have done 600hrs behind this box, and have never had this before. Once in 600 hours qualifies as an intermittent problem. What he was suggesting is that if there was a battery glitch (while the unit was turned off), then it may have lost its *memory* of its position, necessitating the longer start-up time. Normally, you switch it on, and as reliable as clockwork it starts up and is ready in a few minutes. Same during flight. This assumes it remembers where it was when it was switched off. The owner's manual talks about this issue (actually, this is true of all GPS units, both aircraft and personal that I've ever used). I've got two 89 series GPS's on my workbench, one of which will be used for an upcoming experimental installation. My only references into this matter are dealing with those two boxes, and the installation manual for the 89 series. You say the problem is fixed now, as in, not recurred? That's correct. Do you have any user defined waypoints? If there are/were, and are not now, this might point to a problem in the memory (powered by that little battery).. maybe there is an intermittent break in the power supply. You indicated the box was opened within the past few months - could be pertinent in troubleshooting this item. How would the loss of the battery power prevent the GPS getting a satellite lock? See above. It doesn't prevent it really ... but it can make it take longer. Moving the GPS before it's done with this can make it take even longer. Unless somebody can find a clue in the data next to the individual satellites, or the date+time+location, I suspect this is a rare bug in the firmware. That's possible regardless of what people find, I suspect. Of course if it happens again then I have a duff unit... okay. -- Mark Hansen, PP-ASEL, Instrument Airplane Cal Aggie Flying Farmers Sacramento, CA |
#5
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Unusual Honeywell KLN94 aviation GPS failure - what could causethis?
Peter wrote:
How would the loss of the battery power prevent the GPS getting a satellite lock? It doesn't.. It legthens the time required to update its initial position. Pretty much every gps, the first time its turned on, takes a LONG time to obtain enough information to determine its current location. The GPS cant tell you where you are going, or where you ARE, unless it KNOWS where its been (even on a second to second basis). Moving the box while this is happening lengthens that process. If its moved more than 50 miles from its last known position (while powered down) or if the "non-volatile" memory is lost for whatever reason, then this LONG initial startup process occurs while box "finds" itself. Not all of the data required for this is stored internally, and if I remember right, is broadcast concurrently with the various time differential signals that are used to compute the location fix. As long as the machine REMEMBERS where it was, and its first signals indicate that its not moved, the boot-up and acquisition process is quite rapid. For the average end user this is an issue that is never observed, because this sort of thing is seen by the installer during installation, or by the maintenance guy during update/replacement. Rarely, like when the internal battery fails (after many years), an error message is generated by the box that specifies the failure. If you have an intermittent condition that isn't present on power up, it may not annunciate it. Good luck, Dave |
#6
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Unusual Honeywell KLN94 aviation GPS failure - what could causethis?
Peter wrote:
There were no errors showing on the KLN94, other than the lack of a fix. I think this failure is unusual because - as far as I can tell - the SV (space vehicle) signal indications are all normal, but the GPS isn't producing a fix (STATE NAV D). It is as if there was a disconnection between the GPS receiver and the rest of the unit - all this is internal to the KLN94 so ARINC buses don't come into it; the KLN94 doesn't have an ARINC bus anyway, and the KMD550 MFD doesn't use ARINC, it gets the data via RS232. It took an hour to get a fix, which is too long for any kind of slow acquisition. The previous time it was on was about 2 days earlier; a 5 hour flight. If the problem was just showing on the KMD550 then one could understand a bad connection, but this is entirely internal to the KLN94. Satellite geometry can't be the issue because the two other GPSs (one of which was using the same type of rooftop antenna as the KLN94) were receiving fine. The internal KLN94 battery should not be relevant once the power is on. It was also changed a few months ago. Presently I have no idea what this could be. I believe the KLN94 contains a separate GPS receiver module which emits an NMEA stream to the rest of the unit. This stream is in fact accessible via a connector pin on the back of the unit. A break in this stream would account for this issue - but how does the main processor get the SV reception data? I thought that stuff comes down the same NMEA data stream, which is how (nearly) every GPS on the market is able to display the constellation details. I even changed the DME frequencies, while still on the ground, in case it was a DME harmonic messing with the GPS signal (that's a well known one). However, I may not have done that for long enough. The trouble with that theory is that such interference should show up in the SV signals too. The selected VOR/DME would have been 113.4 MHz. I don't know if that is a harmonic of the GPS signal. Also the failure persisted for about an hour, by which time I would have long been tracking a different VOR. Dave S wrote Ooops. Only looked at pic number 1, not the ones showing the sat reception. Only time I've had a slow position computation is when the unit has been powered down for a LONG (weeks to months) time. Takes up to 15 mins for it to "find itself" while remaining still. An intermittent connection on the internal battery (there is a small watch battery on the board inside - at least the KLN-89/B does) to keep last known position and user waypoints stored. You didn't have any error/hardware error messages on startup? Dave Dave S wrote: I have seen that indication when the antenna did not have a clear view of the sky. The installed aircraft was an EADS/Socata TB-9 with gull wing doors. Coming out of the pad, the pilot's door when up (as it was in the summer) would obscure much of the sky and not allow the GPS to get a position. Resolved by removing the blockage by repositioning the plane or lowering the door. The antenna in this case was on the roof of the cabin between the two gull-wing-doors. Peter wrote: http://www.peter2000.co.uk/aviation/kln94-failure/ This unit has been working perfectly for four years, and works fine now. Peter. -- Return address is invalid to help stop junk mail. E-mail replies to but remove the X and the Y. You said the battery was changed a few months ago, then you started having the problem. I wonder if the "repair" was not done well. -- Regards, Ross C-172F 180HP KSWI |
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