Timeline for Is this a glitchy ADS-B signal?
Current License: CC BY-SA 3.0
15 events
| when toggle format | what | by | license | comment | |
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| Dec 15, 2014 at 18:44 | history | edited | DeltaLima♦ | CC BY-SA 3.0 |
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| Mar 19, 2014 at 12:30 | comment | added | KORD4me | @DeltaLima, thanks! | |
| Mar 19, 2014 at 11:46 | comment | added | DeltaLima♦ | @KORD4me 4 to 5 seconds is the typical rotation period of a TMA (TRACON) radar. And that one is allowed to miss a target every now and than as well, so up to 15 seconds occasionally is acceptable. The ADS-B integrity is in the FTC field, first five bits of the 5th octet IIRC. If FTC is 18, there is no position data integrity. I don't know ADSB#, I use home brewed tools. | |
| Mar 19, 2014 at 11:03 | comment | added | KORD4me | @JanHudec thx for the link, I heard of TCA but not TMA, learned something new, thanks! | |
| Mar 19, 2014 at 6:00 | comment | added | Jan Hudec | @DeltaLima: I can kind of see the answer. If the INS was designed before precise GPS was released for civilian use, it probably does not have support for in-flight updates and if the aircraft does not need high RNP there was no need to upgrade to a combined unit that does. | |
| Mar 19, 2014 at 5:52 | comment | added | Jan Hudec | @KORD4me: TMA. | |
| Mar 18, 2014 at 22:38 | comment | added | KORD4me | @DeltaLima, good info, two follow ups (making u earn that check mark!). 1: where is 4 to 5 seconds coming from and 2: what is TMA? Bonus question: do you know exactly where in ADS-B frame is that "invalid" location flag specified, or how one might filter it out using something like ADSB# application? | |
| Mar 18, 2014 at 21:35 | comment | added | DeltaLima♦ | @KORD4me it should not happen very often, preferably not at all. Some airframes have it quite frequently, it is usually related to the GPS antenna. ADS-B is not yet used in KORD or EGLL. The operational impact would be unnoticeable anyway in most cases, since a position update is only needed every 4 or 5 seconds in the TMA. | |
| Mar 18, 2014 at 21:31 | comment | added | DeltaLima♦ | @JanHudec feel free to ask that question | |
| Mar 18, 2014 at 21:10 | comment | added | Jan Hudec | The more important question is why isn't the INS continuously realigned from the GPS. In fact according to some document linked from another question the combined RNP units (especially the RNP0.1 ones) can do that, using each system to filter errors of the other. | |
| Mar 18, 2014 at 20:49 | vote | accept | KORD4me | ||
| Mar 18, 2014 at 20:48 | comment | added | KORD4me | can you comment on how often does this happen if you have a swag and how may ATC deal with these interruptions? Or do they automatically switch to primary radar? | |
| Mar 18, 2014 at 20:17 | comment | added | DeltaLima♦ | They do have two GPS units but each is connected to a different transponder. Transponders are not switched for a momentary glitch in the GPS. | |
| Mar 18, 2014 at 20:09 | comment | added | KORD4me | I could see that. So it's not really that INS is used the whole time, it's that it intermittently switches to INS. I was always under impression that they had redundant GPS units, but maybe both were failing at the same time? | |
| Mar 18, 2014 at 18:46 | history | answered | DeltaLima♦ | CC BY-SA 3.0 |