POSITIONAL ERRORS IN ADSB?

[Roger]

A question (and sorry if it has been asked and answered elsewhere)....

At both Heathrow and Palma (Majorca) recently I have noticed that while most a/c track down the extended centre line on the map perfectly in agreement with where the a/c actually is,  a small number, perhaps 1 in 20, are transmitting an incorrect position. The error is perhaps half a mile to a mile out, although I don't remember many that were only just a little bit out. There is no pattern to which airlines or which a/c type.

Anyone know why some are wrong? If ADSB is being used onboard to give the pilots situational awareness, it doesn't seem too clever for some aircraft to have the system in error.

Roger

[RodBearden]

Hi Roger

This has been discussed many times before! Basically, it's down to position error in the aircraft's navigation equipment. You'll notice it more in older aircraft, for example B733's, and less, if ever, in modern aircraft like B738's which have GPS.

I often get Jet2 B733's landing in the sea off Blackpool, while the Ryanair 738's always land on the runway!

Rod

[Roger]

Thanks - remind me not to fly Jet2 to Blackpool !!

[Allocator]

Anyone know why some are wrong? If ADSB is being used onboard to give the pilots situational awareness, it doesn't seem too clever for some aircraft to have the system in error.

Roger

Roger,

The ADS-B isn't being used by the crew for positional awareness.  It's only there for ATC when they have the correct kit (and us of course!).  It's not mandatory, so there isn't really need to have it at all.  It's future technology that hasn't been fully exploited yet.

[dudbaker]

Hi

Inertia Nav (INS) is used for navigation when no other aids are available.  INS tends to drift over long flights.  Not a problem if you have 60NM seperation.  During the landing phase the crew will be using DME, VOR, ILS and or NDB as available.