phkc070408

This is a technical ops question. I was on holiday in AUS over your winter and we flew ADL-KGC-ADL 2142 of 29-Jul-22 and 2143 of 02-Aug-22. When looking at our flights on FlightRadar24, I noticed that the speed was very inconsistent and bounces around especially during takeoff and landing. In the attached graphs, the KGC end is not displayed, most likely due to unavailable data from a remote / lo volume airport. If you notice, in the takeoff from ADL, there are a few small areas where speed actually decreases.

Using a video I made out the window of our landings and takeoffs, I was able to plot some estimated points by comparing the image out the window to a google maps image, and using the time between points in the video. I got very similar results, with the speed carrying greatly.

A family member is a commercial pilot here in the USA so I asked him about this. His response was that many small aircraft lack auto-throttle and auto-pilot, but he couldn't speak for the QF DH3 (or any DH3 specifically). He said that a lack of these features could definitely cause variations like this. I thought maybe it had something to do with a plane with a smaller powered engine being affected more by the winds. My other theory is that the data is inaccurate most likely due to FR24's lack of access.

If anyone has any technical knowledge about this aircraft, could you please comment on these graphs and let me know what you think? I'd like to use these flights for a presentation project, but don't want to go to the trouble if the data is wrong.

og

Postings on PPRuNe frequently comment on the unreliability of FR24. FR24 relies on whatever (amateur) receivers can pick up the data - so there’s a variability factor in itself. I’d (like to) assume that if the aircraft has unreliable airspeed indications, it’d be a problem and would be in the hangar until fixed.

shillard

Flight radar is not connected to a pitot tube on the front of the aircraft.

It's neither accurate, nor reliable when measuring airspeed.

nzkarit

Note that is ground speeds. Pilots generally fly to an indicated airspeed or mach number.

Being a smaller plane it has less inertia so will accelerate and decelerate faster, than say a wide body. Also what was the wind like? The smaller the plane generally the more it will bounce around more in the wind.

The data source is ADS-B so the speeds and altitudes are coming from the avionics. Not math at the receiver end. If the message is received the data is accurate.

Also it is a dh8c not dh3. That plane is Dash 8-300 not an DHC-3 Otter.

Though also a bit unclear what your question is and your hypothesis for the presentation.

nzkarit

But the transponder is connected to the pitot tube via the avionics. And the transponder is sending the ADS-B messages that FR24 is receiving.

Though in this case the graph is ground speed not air speed so will be coming from the inertia navigation, calculation of wind aloft, and/or GPS.

shillard

Dude the two up front will be looking at the ASI - not Flight Radar.

There's a reason for that.

rtaylore

no wi-fi on QF?

nancypants

Ground speed is surely the answer and nothing to do with the plane at all

for comparison here’s a 737- same issue