PPRuNe Forums - View Single Post - Jet goes down on its way to Medellin, Colombia
Old 3rd Dec 2016, 16:39
  #563 (permalink)  
Airbubba
 
Join Date: Jun 2001
Location: Rockytop, Tennessee, USA
Posts: 5,898
Likes: 0
Received 1 Like on 1 Post
Originally Posted by DaveReidUK
GE plot of the taxy out and take-off.



The ADS-B offset looks pretty close to a mile to me . It's highly likely that a similar offset applies to the published track of LM2933 in the hold, but I agree it's still not enough to put it over the VOR.
You are right (as usual, I'm afraid ). I was looking at the track in this link I posted earlier:

https://www.flightradar24.com/data/a...-2933/#bbef1b9

It doesn't show the taxi at Viru Viru and since most of the shift is aligned with the runway, the track starts near the pavement, perhaps at liftoff.

Flightradar24's blog has this comment on the transponder in the RJ85:

Positional Accuracy

CP-2933 was equipped with an older ADS-B transponder which may be subject to positional accuracy issues. The position of the aircraft is calibrated prior to take off and the on board computer calculates positions based on speed and direction of the aircraft. With certain types of flying (including holding patterns), the calculation can become inaccurate.
Also, FR24 has this playback of traffic in the Medellin area near the time of the mishap:

https://www.flightradar24.com/2016-1.../6.14,-75.5/10

Many of the other planes drop out of ADS-B receiver coverage from time to time and give jagged plots but it appears that they are holding at the VOR while LMI2933 is holding several miles south of the navaid.

Has anyone found other plots of the holding on other ADS-B trackers like RadarBox24 or FlightAware? Also, on the RJ85 are the nav instruments and computers updated with radio nav and maybe as Dave says, the transponder only sends inertial position? The holding pattern does look like it is nicely plotted, just not in the right place.

Originally Posted by PEI_3721
Any 146/RJ operators prepared to admit one of those 'Doh' moments when using the GNS fuel planning page as an inflight guide - 'how goes it', forgetting that the system requires manual updating.
Memory fades, but only part of the system, fuel contents or fuel flow, was automated.
Well, yes; I managed at least one Ooops during in-flight planning. More seriously, witnessed at least two Doh moments, one involving a tech stop to refuel.

Recall the A300 at Vienna landing without fuel; as an industry we tend to forget safety lessons.
It was an A310 at VIE that ran out of gas, but as in this crash, they were very late in confessing the problem to ATC.

Years ago I flew a bizjet, perhaps a Lear, with partially automated fuel tracking and prediction supplied to the nav computers. It was as you described, helpful but a real gotcha if you forgot to initialize it each leg.

And, I've been sitting in a holding pattern in a Boeing, trying to figure when to go to plan B. Obviously, doing rough calculations in my jet-lagged head, and then looking at the FMS prediction. Whatever algorithm the box used made the landing fuel look great when on the inbound leg and then it dropped by several thousand pounds turning outbound.
Airbubba is offline