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 Post subject: Re: Pilatus PC-24
PostPosted: 06 Sep 2021, 06:57 
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Username Protected wrote:
Maybe Pilatus will offer drop tanks so it can make it to Hawaii.

I missed the Hawaii part. Yes, the G-V is definitely the aircraft for that trip versus the PC-24. An old flying buddy flies Falcon 50s on that route but he also has Gulfstream time and loves those planes.

Honestly, if they are talking to a buyer's agent or agency, they likely will also talk G-IV / G-IV SP as slightly less expensive aircraft to operate. There may be some older G450s for somewhere in the ballpark of a G-V that is 7-10 years older.


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 Post subject: Re: Pilatus PC-24
PostPosted: 06 Sep 2021, 07:32 
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Username Protected wrote:
Doubtful that the 680 or 750 could do Hawaii without a wet footprint, even from California.

680 can. Textron specifically analyzed this for engine failure at worst possible point and making landfall within 180 minutes.

http://www.aero-news.net/index.cfm?do=m ... 2bdd3bbb1c

The 680 can do some long range flights, like 2865 nm discussed here:

https://investor.textron.com/news/news- ... fault.aspx

Mike C.


From the first article:

Quote:
Cessna Engineering conducted an analysis using worst case weight and determined the Model 680 Sovereign is capable of travelling a distance of 1,022 nm in 180 minutes (under standard conditions in still air) after an engine failure.


How often will there be still air?

I'm not saying the 680 can't ever do CA-HI, but there will be plenty of times it can't do it safely.

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 Post subject: Re: Pilatus PC-24
PostPosted: 06 Sep 2021, 09:01 
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Username Protected wrote:
The first article mentions a cruise altitude of 25,000 feet if an engine is lost.

That was only necessary to establish it meets 180 minute ETOPS. Textron did that by simply pushing the throttles up on the good engine instead of using max range OEI settings. Thus, no changes to the airplane, just a new procedure which maximizes speed versus range when OEI.

Now that it does meet ETOPS, the flight can dispatch, but once airborne, the pilots can opt to fly the OEI portion however they want.

Quote:
No mention of loss of pressurization. I hope everyone has a three hour supply of oxygen.

They can reach Hawaii at 15,000 ft OEI. It will take longer than 180 minutes, however. No oxygen needed.

I don't believe ETOPS is predicated on both an engine failure and a pressurization failure at the same time.

Mike C.

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 Post subject: Re: Pilatus PC-24
PostPosted: 06 Sep 2021, 09:11 
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Username Protected wrote:
How often will there be still air?

Wind changes the equal time point to be closer/further from Hawaii. Say there is a 100 knot headwind westbound. The ETP will be ~300 nm closer to Hawaii (180 minutes of wind). Engine fails at ETP means you can make it to Hawaii at 100 knots ground speed less than still, or make it to the mainland at 100 knots more than still air speed.

Of course, the wind could be mostly cross, which hurts speed in both directions. But even then, the 680 can make the crossing safely since it can fly a lot longer than the 180 minute ETOPS criteria.

Quote:
I'm not saying the 680 can't ever do CA-HI, but there will be plenty of times it can't do it safely.

It can do it safely. Meeting the ETOPS standard doesn't force the crew to use the procedure to establish ETOPS.

The 680 has 3200 nm range doing a 2000 nm trip. Plenty of margin. It can have an engine failure and a pressurization failure and make it to land from the worst possible point on the flight.

Mike C.

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 Post subject: Re: Pilatus PC-24
PostPosted: 06 Sep 2021, 09:14 
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But if the wind is really strong, there will be a gap between the ETP's. That is called a wet footprint. If there is an issue in the wet footprint, the airplane may not be able to reach either ETP airport.


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 Post subject: Re: Pilatus PC-24
PostPosted: 06 Sep 2021, 09:31 
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Username Protected wrote:
But if the wind is really strong, there will be a gap between the ETP's. That is called a wet footprint. If there is an issue in the wet footprint, the airplane may not be able to reach either ETP airport.

The 680 with 3200 nm range doing a 2000 nm trip will be able to reach one of the airports. There is no wind ever observed on the Earth which will prevent that.

The only thing that may change is the ETOPS criteria of 180 minutes from ETP to an airport may not be met. This does not prevent the airplane from reaching an airport in actual flight, however, since it can fly OEI much longer than 180 minutes.

Mike C.

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 Post subject: Re: Pilatus PC-24
PostPosted: 06 Sep 2021, 09:38 
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Username Protected wrote:
But if the wind is really strong, there will be a gap between the ETP's. That is called a wet footprint. If there is an issue in the wet footprint, the airplane may not be able to reach either ETP airport.

The 680 with 3200 nm range doing a 2000 nm trip will be able to reach one of the airports. There is no wind ever observed on the Earth which will prevent that.

The only thing that may change is the ETOPS criteria of 180 minutes from ETP to an airport may not be met. This does not prevent the airplane from reaching an airport in actual flight, however, since it can fly OEI much longer than 180 minutes.

Mike C.


That's not true, but I'm running out of steam arguing with people on the internet.

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 Post subject: Re: Pilatus PC-24
PostPosted: 06 Sep 2021, 12:53 
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Username Protected wrote:
Doubtful that the 680 or 750 could do Hawaii without a wet footprint, even from California.

I was under the impression it's possible, but maybe it's a little tight. SFO-HNL is 2,084nm; a 680 or 750 should be able to do at least 3,000nm with IFR reserves. Worst-case scenario would probably be losing pressurization and having to descend to FL 150 mid-way. Let's say 1,100nm to get to dry land. They would still have 2/3 their fuel, but if nm/lb goes down by more than a factor of two, that could be interesting. And there are probably some regulations I'm not aware of.

Better bring big O2 bottles for the passengers (like 3 hours worth) and keep it up high, if that's even legal.

Revisiting what I wrote above, I don't have a Sovereign manual, but using the 501 as an example, mileage only drops by a factor of about 1.7 when you drop from FL 410 to FL 150. That's on two engines. You might be able to get an extra 10% mileage if you shut down one engine.

So, it does look like there should be enough fuel to make it to an airport pretty comfortably if you lose pressurization mid-point and have to descend to FL 150 (with zero winds). Based on OEI speed and fuel flow as noted below, I calculate 1.3 hours fuel remaining after arriving at HNL or SFO.

However, if you're heading to Hawaii and had a 100kt headwind, your critical point (equal time to land distance) assuming 265kts OEI cruise speed at FL150 will be about 649 nm to HNL and 1435 nm to SFO. Problem is, how much fuel do you have left at the critical point? Normal cruise speed is about 450kts, but with the headwind you're only doing 350. So you're 1435/350=4.1 hours in. Normal max endurance is 3200nm/450kts = 7.1 hours. So you have 3 hours of fuel left.

Continuing to HNL at 265 KTAS OEI at FL 150, your ground speed is 165 kts and you need to go 649nm. That's 3.9 hours.

Although your fuel flow is less on one engine, one engine at FL 150 at 265 KTAS uses only about 1.1 times less fuel per hour than two engines total at FL 410 at 450 KTAS. So instead of running out of fuel in 3 hours you will run out in 3.3 hours.

However, you will flame out a mere 105 nm from HNL, assuring a relatively timely rescue.
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 Post subject: Re: Pilatus PC-24
PostPosted: 06 Sep 2021, 14:14 
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I thought he said Houston to Hawaii…

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 Post subject: Re: Pilatus PC-24
PostPosted: 06 Sep 2021, 14:29 
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Username Protected wrote:
Further on the PC-24 noise issue:

On 6/18/21 at 10:22 local time a PC-24, N281EB departed SMO and read an astounding 98.9 dB. This is 157 percent of allowable and the highest number I ever remember for a Stage 3 airplane. A Lear 25 reads lower than that. A Gulfstream II reads lower than that.

Another PC 24, departed SMO on 6/17/21 at 13:24 local and read 95.7 dB which is 108 percent of allowable. That is believable and probably a matter of technique.

But 98.9 is incredible.

As a comparison, I used to consistently get Gulfstream IV's out of SMO, fueled for the east coast at or below 89.0 dB or 50 percent of allowable.

I think the PC-24 is going to have noise issues at a great many airports.


Howard,
Those sound levels reported for the 24 are interesting. Pilatus documents the noise levels in the AFM and the highest noise level listed is 92 EPNL, EPNdB with no special procedures to meet that level. There are a few differences in the 24’s engines compared to other Williams installs.

- The 24 has different exhaust nozzles that use Williams Exact thrust vector technology and the Coanda effect to create a upward thrust vector.

- The aircraft has Automatically Thrust Reserve (ATR) which gives an additional ~200#s of thrust per engine for emergency conditions requiring more thrust such as an engine failure. ATR can be manually selected by pushing the thrust levers forward past a hard detent for conditions such as a wind shear escape. Maybe pilots accidentally took off in ATR mode?

Where is your data source? I’d be interested to see what a CJ4 reports as it has relatively the same FJ-44-4A engines. I’d also be interested in seeing the variance between 24s departing from that airport.

When a noise limit is busted, are pilots notified?


I am not clear what data source you are asking for. The planes took off at the dates and times I reported and read the numbers I reported.

That is public record.

I don't remember any CJ4 busting, but could easily be wrong about that. However, CJ's usually comply.

If you will look back in this thread I explain that two planes with identical engines may have very different results. It is not about the engines.

When a plane violates the noise limits at SMO, a notice is sent to the registered owner at the address in the FAA database. First violation results in a warning, second and third in fines and fourth violation in banning that particular airplane.

However, if enough planes of the same model violate, the City will attempt to have all planes of that model banned.
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Last edited on 06 Sep 2021, 15:04, edited 1 time in total.

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 Post subject: Re: Pilatus PC-24
PostPosted: 06 Sep 2021, 14:41 
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Ian wrote


"Revisiting what I wrote above, I don't have a Sovereign manual, but using the 501 as an example, mileage only drops by a factor of about 1.7 when you drop from FL 410 to FL 150. That's on two engines. You might be able to get an extra 10% mileage if you shut down one engine.

So, it does look like there should be enough fuel to make it to an airport pretty comfortably if you lose pressurization mid-point and have to descend to FL 150 (with zero winds). Based on OEI speed and fuel flow as noted below, I calculate 1.3 hours fuel remaining after arriving at HNL or SFO.

However, if you're heading to Hawaii and had a 100kt headwind, your critical point (equal time to land distance) assuming 265kts OEI cruise speed at FL150 will be about 649 nm to HNL and 1435 nm to SFO. Problem is, how much fuel do you have left at the critical point? Normal cruise speed is about 450kts, but with the headwind you're only doing 350. So you're 1435/350=4.1 hours in. Normal max endurance is 3200nm/450kts = 7.1 hours. So you have 3 hours of fuel left.

Continuing to HNL at 265 KTAS OEI at FL 150, your ground speed is 165 kts and you need to go 649nm. That's 3.9 hours.

Although your fuel flow is less on one engine, one engine at FL 150 at 265 KTAS uses only about 1.1 times less fuel per hour than two engines total at FL 410 at 450 KTAS. So instead of running out of fuel in 3 hours you will run out in 3.3 hours.

However, you will flame out a mere 159nm from HNL, assuring a relatively timely rescue.[/quote]

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

Equal Time Point is just that, at that point, under a specified condition it will take the same time and fuel to either continue or return.

The formula for ETP is:

Distance to ETP=total distance times GS back / (GS forward + GS back).

A computer flight plan will identify the geographical point in lat and long that can be entered as a waypoint but is accurate only if the conditions of the calculation are maintained, i.e. the ground speeds and cruise fuel flows for fuel remaining at destination or the diversion airport

A maximum range is achieved at a specific speed/AOA and requires a certain amount of thrust/fuel flow. To maintain a speed on one engine that would be maintained on two engines requires a doubling of the fuel flow on the one engine. So I don't see how better range can be achieved on one engine vs two.

The old trick for flying and ILS in a jet if an engine quits is just look over and double the fuel flow on the remaining engine to maintain speed. Same with a 4 engine jet; three remaining engines have to have the fuel flow 4 had.


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 Post subject: Re: Pilatus PC-24
PostPosted: 06 Sep 2021, 15:03 
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Except if they go OEI at 15 K ft in your 100knot wind scenario, they are not going to either SFO on HNL,
They are going to the closest wind adjusted airport.

Hilo or Santa Barbra


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 Post subject: Re: Pilatus PC-24
PostPosted: 06 Sep 2021, 15:04 
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Username Protected wrote:
A maximum range is achieved at a specific speed/AOA and requires a certain amount of thrust/fuel flow. To maintain a speed on one engine that would be maintained on two engines requires a doubling of the fuel flow on the one engine. So I don't see how better range can be achieved on one engine vs two.

Fuel flow and thrust are not really linear in relationship. Turbine engines get more efficient at higher throttle.

Most of the time, the trip is done far faster than max range speed and thrust, the passengers want to go fast, so when the engine quits, you go slower and more efficiently. This gives the impression range is improved with one engine when it really isn't.

Quote:
The old trick for flying and ILS in a jet if an engine quits is just look over and double the fuel flow on the remaining engine to maintain speed. Same with a 4 engine jet; three remaining engines have to have the fuel flow 4 had.

Doesn't work on Citation sized planes from what I can tell.

This is also maintain the same speed, not slowing to a more efficient cruise speed.

Mike C.

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 Post subject: Re: Pilatus PC-24
PostPosted: 06 Sep 2021, 15:23 
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Username Protected wrote:
Except if they go OEI at 15 K ft in your 100knot wind scenario, they are not going to either SFO on HNL,
They are going to the closest wind adjusted airport.

Hilo or Santa Barbra

I still think they're going swimming.

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 Post subject: Re: Pilatus PC-24
PostPosted: 06 Sep 2021, 16:44 
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Nobody should go swimming because the minimum fuel required is to reach either airport from the ETP. In the case of a twin it would be fuel for low level from the ETP. For 4-engine planes, the 3 and 4 engine ETPs are usually the same, with 2 engines out or loss of pressurization, the low level ETP fuel is required which is the most restrictive.


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