TBM900 verses PC12NG range performance comparison

This post was prompted due to a recent Flyingmag article which presents quite inaccurate information regarding these two aircraft. The article I refer to was this one:

Daher-Socata TBM 900 Versus the World: Comparison Specs
By Flying Staff / Published: Jun 04, 2014
http://www.flyingmag.com/aircraft/turboprops/daher-socata-tbm-900-versus-world-comparison-specs

This post is intended to put the basic verifiable facts on the table so others can get a clearer view of what the comparative performance differences are. What immediately stood out within the article was the "IFR Range" quoted, where they assert the IFR range of the PC12NG is only 1,309 nm, or about 250 nm less than the verifiable IFR range.

As I'd recently examined both aircraft's POH's quantitatively within a range assessment model I knew these asserted IFR ranges for the TBM900 were being greatly exaggerated. Flightmag claims (without qualification) the TBM has an IFR range of 1,585 nm, but the TBM900 AFM tables easily demonstrate that this in not the case.

I constructed the model several years ago specifically to test such claims against the published AFM data for various conditions and configs. The model takes into account taxi fuel for departure and arrival, the number of landing points (it's also linked to an external flight planner) plus the POH's measured fuel burn rate, speeds and distance, for both climb and descent. It then takes into account the remaining useable fuel plus the known fuel burn curve against speed from LRC to maximum cruise, for any desired altitude, to determine range value and reserve buffers.

It can be set for any ISA condition, weight and fuel flow, you just plug in the AFM numbers and it reports and graphs the result. In short, it accurately calculates and plots aircraft range performances. It's accurate and represents measured performances. It's also ideal for comparing different aircraft to determine more precisely what their performance differences are. What's provided below can be verified for the TBM900 via simply looking up the AFM tables to see if the values are consistent.

So the following is what emerges when you compare a TBM 900 to the PC12NG:

Firstly, the TBM900:

Fuel Burn Profile Estimator *ISA+20 **FL280 7,100 lb (5-blade prop)

Max Cruise | STD Cruise | Econ Cruise | Long-Range Cruise
316 | 293 | 271 | 248 KTAS
214.2 | 193.1 | 172.3 | 150.60 l/hr
850 | 935 | 1,030 | 1,144 nm

The last line is the 120 min reserve IFR range for each respective speed setting.

A climb and descent profile is calculated thus using AFM values:

Climb Calculator | Descent Calculator

Climb to feet 28,000 | 28,000 Descent from feet
Climb Speed KTAS 170 | 240 Descent Speed KTAS
Climb feet/min 1,675 | 2,000 Decent feet/min
Climb Time mins 16.7 | 14.0 Descent Time mins
Climb Distance nm 42.9 | 73.4 Descent Distance nm
Climb Fuel Used L 114.0 | 40.6 Descent Fuel Used L

The resulting TBM900 IFR range calculates out as follows for FL280:

***VFR 1,454 nm 1,105.2 L @ 248 kt 1 POB 45 min VFR res
IFR 1,330 nm 1,105.2 L @ 248 kt 1 POB 75 min IFR res
IFR 1,268 nm 1,105.2 L @ 248 kt 1 POB 90 min IFR res
IFR 1,144 nm 1,105.2 L @ 248 kt 1 POB ****120 min IFR res

NOTES:

* I use the ISA+20 tables for these calculations in order to obtain a real world performance estimate as this is a typical condition encountered for about 6 months of the year where I fly.

** Robert Goyer's separate Flyingmag TBM900 flight test article states that the optimal operating altitude for the TBM900 is FL280 (as opposed to FL260 for the TBM850) so I calculated the POH range and fuel burn for FL280, but at ISA+20.

*** It's quite ridiculous to quote maximum range of a turboprop in "45 min VFR" terms when the max range can only be achieved using a max-altitude IFR flight plan and thus a mandatory IFR reserve. So that sort of dodgy blurb does such companies no credit. Indeed Pilatus did the very same thing claiming 1,830 nm max range with a 45 min "VFR" reserve.

But Daher Socata's "TBM 900 IN FIGURES" pdf doc states the "Maximum range with maximum fuel (ISA conditions, MTOW, no wind, one pilot, 45 min fuel reserve) @ 31,000 ft. 252 KTAS cruise speed 1,730 NM 3,304 km"

But the AFM at ISA+20 reveals the achievable range figure implied is 1,445 nm with a "45 min VFR" reserve allocation. Which is 285 nm less range than what the marketing document claims. Now I could redo the calculation at ISA, but a difference of 285 nm is not just going to evaporate if I do. So many articles just repeat the exaggerated marketing claims which are substantially at odds with what the AFM indicates the aircraft can actually achieve. Readers need to be aware that such lazily constructed and inaccurate articles are common and comparisons should be checked.

**** 120 min reserves is typical for remote area cross-country flights where I am, so it's a normal reserve load for many if not all such flights. That sort of requirement is not true for other countries where IFR airports and jet refuellers are situated closer together. But as this is a real-world estimate of range several IFR reserve flight-time sizes and resulting calculated range values are supplied so a direct range comparison between TBM900 and PC12NG is valid and useful for less remote areas, also.


That's the TBM900 done so I'll now provide the same information and subsequent range values for the PC12 using the same conditions from its AFM data tables. I've done this for two altitudes for the PC12, namely FL250 and FL170 simply in order to illustrate the superior range flexibility at both IFR and VFR altitudes. Note that FL250 to FL260 is about the ideal speed-range altitude tradeoff for the PC12NG so I'll restrict the analysis to altitudes which would be typically used in real-world operations.

So, for the PC12:

Fuel Burn Profile Estimator ISA+20 9,200 lb (i.e. typical TOW for 1 x POB + full-fuel)

Conditions FL170 @ ISA+20, where LRC = 225 kt
Max Cruise | STD Cruise | Econ Cruise | LR Cruise
256 | 246 | 235 | 225 KTAS
238.3 | 226.4 | 215.0 | 206.2 l/hr
1,031 | 1,067 | 1,098 | 1,115 nm

The last line is the 120 min reserve IFR range, for each respective speed setting.

So the same at FL250:

Conditions: FL250 @ ISA+20 9,200 lb, where LRC = 216 kt

Max Cruise | STD Cruise | Econ Cruise | LR Cruise
247 | 237 | 226 | 216 KTAS
186.6 | 175.6 | 165.2 | 157 l/hr
1,428 | 1,482 | 1,530 | 1,560 nm

The last line is again the 120 min reserve IFR range for each respective speed setting at FL250.

The climb and descent profile was calculated using these AFM charted values:

Planned Climb Climb Calculator | Descent Calculator Planned Descent
Climb to feet 25,000 | 25,000 Descent from feet
Climb Speed KTAS 175 | 220 Descent Speed KTAS
Climb feet/min 1,000 | 2,000 Decent feet/min
Climb Time mins 25.0 | 12.5 Descent Time mins
Climb Distance nm 66.0 | 60.0 Descent Distance nm
Climb Fuel Used L 99.3 | 35.4 Descent Fuel Used L

The resulting PC12NG range is calculated as follows:

FL170 1,284 nm 1,521.2 L usable @ LRC, 1 POB and 75 min IFR res
FL170 1,228 nm 1,521.2 L usable @ LRC, 1 POB and 90 min IFR res
FL170 1,115 nm 1,521.2 L usable @ LRC, 1 POB and 120 min IFR res

... and for FL250;

FL250 1,722 nm 1,521.2 L usable @ LRC, 1 POB and 75 min IFR res
FL250 1,668 nm 1,521.2 L usable @ LRC, 1 POB and 90 min IFR res
FL250 1,560 nm 1,521.2 L usable @ LRC, 1 POB and 120 min IFR res

So the evidence from the respective AFM's for the TBM900 and PC12 is clear-cut, it wildly differs from that given in the linked Flightmagazine article. It's of course not just that one article which prompted me to do this analysis, rather its because many similar aviation blogs are routinely producing obviously inaccurate numbers, due to a lack of fact checking.

Apparently checking basic numbers generally does not occur, which is a shame as it's that checking and care to get them right which generates credibility (and readership), while failing to do so sheds both. Obviously we can't be right or knowledgeable at all times, in all respects, but we can do a lot better than no fact-checking at all. This is becoming much too common in aviation articles churned out, today.

The actual range comparison is as follows:

TBM900 = 1,144 nm
FL280, 248 KTAS, 1,105.2 L useable @ 248 KTAS ISA+20, 1 POB & 120 min res.

PC12NG = 1,560 nm
FL250, 216 KTAS, 1,521.2 L usable @ 216 KTAS ISA+20, 1 POB & 120 min res.

It's really not that hard to get the numbers right and make comparisons meaningful and useful. If that's not the aim then why write a comparison article?


CONCLUSIONS:

(1) The PC12's range dramatically exceeds that of the TBM900, at ISA+20. Indeed if you average out the burn curve the PC12 has a whopping 51.6% more range than the TBM900. Which reveals Flightmag's comparison "IFR Range" values to be wildly inaccurate, even at a first glance.

(2) But in order for the TBM900 to achieve its maximum IFR range at ISA+20, it must slow its speed to 32 knots below the quoted max cruise speed of a PC-12. Long-range fast ~300 kt cruise is the fiction you're sold but the reality is a bit different.

(3) But here's the real kicker, if you then fly the PC12 at the same speed as the TBM900 (248kt) the PC12 still has 1,428 nm of range (the TBM900 only 1,144 nm) so the PC12 can reach 284 nm further, at the TBM900's speed!

(4) But the bigger kicker is the TBM's purported speed advantage over a PC12NG is rendered non-existent as a PC12 is just as fast as the TBM900 on max range flights and can fly much further after the TBM's already run dry.


There are reasons why one of these aircraft costs $800,000 more than the other, which is just the sort of thing a comparison reader or a flight-test reader might want to know.

Went back over the respective AFMs and checked the ISA+20, 1 x POB, full-fuel TOW figures for both aircraft. I did this at four altitudes and four speeds then tabulated the result and created the following animated .gif to better illustrate the stark difference in fuel burn with speed and altitude, for the two aircraft.



As you see the TBM design is optimized for two things:

1) high-altitude, high-speed sprint to ~850 nm.

2) 250 knot cruiser to ~1,250 nm.​

The TBM900 engine is inefficient below 20k feet hence it's range and flexibility constraints - it was tailored for high-flying between sealed surfaces. The PC-12 NG engine and airframe, on the other hand, were optimized for excellent performance at all altitudes, but its best speed-range performance trade-off is around FL260. Yet speed and range at lower altitude remains exceptional, i.e.

10,000 feet for max speed of 260 KTAS yields 740 nm range with 120 mins reserves at 260 KTAS, on top. And for the TBM900 it's 10,000 feet for a max speed of 274 KTAS, for 384 nm range, with another 120 mins reserves at 274 KTAS.

In other words, the PC-12 NG has 193% more range than the TBM900 at 10,000 ft, ISA+20.

The only clear weakness of the PC-12 NG is at its maximum FL300 altitude, where the LRC speed falls to 214 KTAS, as opposed to a 257 KTAS LRC for the TBM900 at FL310. But even in that case the PC-12 still has 137% more range than a TBM900, with another 120 mins IFR reserve at 214 KTAS.

It loses to the PC-12 range performance even at the altitude the TBM900 was optimized for.


Just the facts, ma'me.