Flight testing ForeFlight’s new performance models

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One of the biggest upgrades in ForeFlight version 9.1 (released earlier this month) is the availability of highly detailed performance profiles. These pre-loaded aircraft data sets allow the app to calculate extremely accurate numbers for time en route and fuel burn, which is a critical feature for high performance and turbine airplanes. Just how accurate are these profiles? We tested it out on a long trip recently – here’s what we found.

Trip One

The first trip was a 780 mile flight from Cincinnati to Pierre, South Dakota, in a Pilatus PC-12. As one of the most popular turboprop airplanes flying today, this offers a fairly representative test of the new performance profiles on a fairly typical flight.

To get started, we used the updated Flights tab in ForeFlight to create a flight and pick an altitude (using the Altitude Advisor and Route Advisor features). We set our estimated time of departure and then entered the fuel and passenger load. ForeFlight predicted (the night before) a flight time of 3 hours and 17 minutes and a total fuel burn of 1421 lbs.

We checked this against Garmin Pilot (which, to be fair, uses more basic performance profiles entered by the pilot), and it predicted 3 hours and 15 minutes and 1362 lbs. of fuel.

We also entered the flight into Fltplan.com, which has been the gold standard for years when it comes to accuracy. It estimated 3 hours and 23 minutes and 1443 lbs. at FL220 (our planned altitude).

So who won? The actual flight took 3 hours and 21 minutes (according to the 30 knot groundspeed flight timer) and used 1403 lbs. of fuel (according to the built-in fuel totalizer).

  • ForeFlight was within 4 minutes of the actual time (under) and 1% of the actual fuel burn.
  • Garmin Pilot was within 6 minutes of the actual time (under) and 3% of the actual fuel burn.
  • Fltplan.com was within 2 minutes of the actual time (over) and 3% of the actual fuel.

Trip Two

The second test leg was a long one – nearly double the first flight – which made it a good test of long range accuracy. The flight was in the same Pilatus PC-12, from Coeur d’Alene, Idaho, to Cincinnati, Ohio, at 27,000 feet.

We planned the entire flight on our iPhone this time, to test how things work on a smaller screen. It was actually quite good. We first entered a basic route in the Routes page, then used the arrow button to send that route to Flights. From there, we could calculate the time and fuel burn, just like we did on the iPad: 5 hours and 35 minutes and 2025 lbs. of fuel.

After planning the flight, we pulled up a Navlog to review the details of the flight, then requested a full briefing from the Flights page. This includes all the essential weather information, including winds aloft along the proposed route:

 

Next we filed the flight plan (again, from the Flights page):

The whole process worked quite smoothly on iPhone, and we had the flight planned, briefed and filed in less than 10 minutes.

For comparison, Garmin Pilot estimated 5 hours and 31 minutes en route and 1982 lbs. of fuel:

Fltplan.com estimated 5 hours and 39 minutes and 2155 lbs. of fuel at FL270.

The results were very close again: 5 hours and 36 minutes en route and 2021 lbs. of fuel used.

  • ForeFlight was within 1 minute of the actual time (under) and an astonishing 0.2% on the fuel burn. Luck probably played a role here, but those are still amazing numbers for a 1500 mile flight.
  • Garmin Pilot was within 5 minutes (under) and 2% of the fuel burn.
  • Fltplan.com was within 3 minutes of the actual time (over) and 7% of the fuel burn.

Conclusions

It’s important not to read too much into a couple of flights. While our tests were representative, there are hundreds of airplane models and thousands of routes (these two flights were fairly direct routing, for example). However, our results suggest that ForeFlight’s new performance models are awfully good – within a couple percent on both time and fuel. In fact, the differences in both time and fuel burn were so small as to be insignificant and easily explained by a last minute ATC re-route or differing pilot technique.

Anecdotal evidence from five other turbine airplane operators we’ve talked to shows the same results too. So for any high performance airplane owner curious about ForeFlight’s new Performance Plus subscription plan, we can give it an initial thumbs up.

Having said that, Fltplan.com was also quite accurate on both flights and even Garmin Pilot’s more basic models were pretty close too. In the end, the most notable takeaway from our test flights may be how great all these aviation apps are. It certainly has simplified long distance flights.

1 COMMENT

  1. FF is great
    the big problem i have found with FF is
    when using the standard/regular FF for piston planes the performance values to be entered as default speeds for climb, cruise, descents are in TAS
    i contacted FF and was told that the TAS is entered as default and is used at and for all altitude speed calculations..
    this is totally wrong,,, how can a variable value such at TAS ( which increases with altitude ) be used as a fixed value as IAS would be in a climb , cruise , descent?? ,, it can t
    the enroute times would always be wrong and so would every other number that FF spits out
    FF needs to add to the program an E6B to calculate the IAS used as per POH etc into TAS for times of trip, fuel burn etc based on altitude and temps
    i hope that helps :))

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