5 ms·

> this has happened before, and I don’t recall any plane accidents then ADSB (the "non-gps" radio signals you mention) broadcasts the planes location... source

by dsl 8y ago

> this has happened before, and I don’t recall any plane accidents then ADSB (the "non-gps" radio signals you mention) broadcasts the planes location... sourced from GPS. Because of deployment requirements there are tons of sub-$2000 ADSB out boxes on the market now that didn't exist in 1999, and hardware wise they are a race to the bottom. (Edit: I also just realized the software could have been written by someone who wasn't alive in 1999). I don't think anything is going to happen. But I also don't like saying nothing is going to happen, because that is when you get a complex failure.

7952 8y ago
I think the parent meant radio beacons on the ground. These give an angle or distance to a known location. ADSB does broadcast the planes location. But this is only used in a very limited fashion. ATC use radar as the main source of information.
- dsl 8y ago
  ADSB is how planes see each other without relying on ATC, and feeds collision avoidance systems. The FAA instructs pilots to believe these systems over ATC because it updates faster than radar. In a very hypothetical worst case scenario, a malfunctioning ADSB transmitter could suddenly put itself right in the path of a large commercial aircraft, forcing it to make dangerous maneuvers to avoid a collision.
  - sho 8y ago
    TCAS[1] doesn't rely on GPS though, it builds a picture of the airspace around it through triangulation and radar-style ranging - I believe it only relies on altitude to be reported by the other aircraft, which is generally very accurate. I suppose anything is possible, but I've never heard of it actually getting plane positions wrong due to sensor malfunctions. Far more likely is pilots not following, or improperly following, its warnings. It's not capable of assuming control over the plane, as far as I know... [1] https://en.wikipedia.org/wiki/Traffic_collision_avoidance_system https://en.wikipedia.org/wiki/Traffic_collision_avoidance_sy...
- yread 8y ago
  Lots of smaller airports use only secondary radar - adsb
correnos 8y ago
I think parent was talking about navigation more than surveillance, so VORs and similar. Between that and inertial navigation, there's plenty of other location sources if your GPS receiver does fail. Though if we're feeling pessimistic, we can guess at how a failure might occur. Let's say that your GPS receiver is poorly written enough that it just starts returning wrong location data on week rollover. Let's also say that that receiver is the aircraft's main time provider. Since the inertial navigation system also needs an accurate time source, it could be hooked up to this same time source. Hopefully it wouldn't be, but we're assuming the aircraft in question here is all-around subtly defective. The INS doesnt't include handling for bogus time jumps, so its speed and location tracking is also corrupted. So, you and your unfortunate copilot could find yourselves without your two main navigation sources a few hours into a trans-pacific flight, and assumedly the GPS-coupled autopilot had pointed you well off course before you'd noticed. In this situation you'd have to get yourselves reoriented based off your compass and best guess of a location. Hopefully you have enough fuel reserves after you little diversion to find land search for an airfield. So that would be a pretty bad situation. I wouldn't worry though, aircraft systems are generally better isolated than that.

by dsl 8y ago

7952 8y ago

I think the parent meant radio beacons on the ground. These give an angle or distance to a known location. ADSB does broadcast the planes location. But this is only used in a very limited fashion. ATC use radar as the main source of information.

dsl 8y ago
ADSB is how planes see each other without relying on ATC, and feeds collision avoidance systems. The FAA instructs pilots to believe these systems over ATC because it updates faster than radar. In a very hypothetical worst case scenario, a malfunctioning ADSB transmitter could suddenly put itself right in the path of a large commercial aircraft, forcing it to make dangerous maneuvers to avoid a collision.
- sho 8y ago
  TCAS[1] doesn't rely on GPS though, it builds a picture of the airspace around it through triangulation and radar-style ranging - I believe it only relies on altitude to be reported by the other aircraft, which is generally very accurate. I suppose anything is possible, but I've never heard of it actually getting plane positions wrong due to sensor malfunctions. Far more likely is pilots not following, or improperly following, its warnings. It's not capable of assuming control over the plane, as far as I know... [1] https://en.wikipedia.org/wiki/Traffic_collision_avoidance_system https://en.wikipedia.org/wiki/Traffic_collision_avoidance_sy...
yread 8y ago
Lots of smaller airports use only secondary radar - adsb

correnos 8y ago

I think parent was talking about navigation more than surveillance, so VORs and similar. Between that and inertial navigation, there's plenty of other location sources if your GPS receiver does fail. Though if we're feeling pessimistic, we can guess at how a failure might occur. Let's say that your GPS receiver is poorly written enough that it just starts returning wrong location data on week rollover. Let's also say that that receiver is the aircraft's main time provider. Since the inertial navigation system also needs an accurate time source, it could be hooked up to this same time source. Hopefully it wouldn't be, but we're assuming the aircraft in question here is all-around subtly defective. The INS doesnt't include handling for bogus time jumps, so its speed and location tracking is also corrupted. So, you and your unfortunate copilot could find yourselves without your two main navigation sources a few hours into a trans-pacific flight, and assumedly the GPS-coupled autopilot had pointed you well off course before you'd noticed. In this situation you'd have to get yourselves reoriented based off your compass and best guess of a location. Hopefully you have enough fuel reserves after you little diversion to find land search for an airfield. So that would be a pretty bad situation. I wouldn't worry though, aircraft systems are generally better isolated than that.