Keystone Navajo Accident in Thompson

[Big Pistons Forever]

If you go to the PA 31 -350 POH section 4, Normal Procedures, the first item on the Normal Takeoff Checklist is "Throttles .......Full Forward".

The second item is "Manfold Pressure ....43 inches ( under ISA conditions)". The amplified instructions further defines this as "take off power"

Operating this aircraft with less than full throttle on takeoff or with engines that are adjusted to produce less than 43 inches of manifold pressure under ISA conditions, is operating this aircraft contrary to the POH.

[rigpiggy]

Short answer is : It uses a density controller at max power settings. As altitude increases the turbo will increase manifold pressure to maintain rated horsepower of the engine. The density controller compensates for temperature and pressure. The idea is that all performance charts are calculated on rated horsepower 310 325 350 Hp If you don't firewall the throttle the density controller cannot do its job and you have no idea how much power you are developing.

Isn't that the whole idea of partial power take-offs ? The density controller might not do its job, so you won't have max power, but you are doing a partial power take off so you "don't care" about the exact power.

Why would this be bad for the engine ?

Because you don't have the extra fuel for cooling

[Donald]

Part power take-offs have been used in the airlines for years now, with sometimes disastrous consequences,, especially when the take-off weight is miscalculated
Why anyone would do a reduced power take-off in a navajo is beyond me

Hahahaha....this is gold.

[GyvAir]

Short answer is : It uses a density controller at max power settings. As altitude increases the turbo will increase manifold pressure to maintain rated horsepower of the engine. The density controller compensates for temperature and pressure. The idea is that all performance charts are calculated on rated horsepower 310 325 350 Hp If you don't firewall the throttle the density controller cannot do its job and you have no idea how much power you are developing.

Isn't that the whole idea of partial power take-offs ? The density controller might not do its job, so you won't have max power, but you are doing a partial power take off so you "don't care" about the exact power.

Why would this be bad for the engine ?

Wouldn't you care even more about the exact power being produced if you were doing a part power take-off?
If I'm going to cut the margin of safety on something, I'm going to want to measure that margin with as much or more precision as if I was working at maximum margin. At some unknown partial power, how are you going to calculate your take-off performance?
As far as I know, there are no part power take-off charts or formulas out there for a PA31 and if there were, there wouldn't be a line for "Unknown Partial Power"

The reason why one needs to put the throttles full forward in the Navajo is because the FCU meters extra fuel for cylinder cooling and detonation prevention. The way it does that is by opening an extra orifice in the FCU, that is only achieved by having the throttle physically forward. It works in conjunction with the mixture control. I remember seeing a picture somewhere but I cannot find it now.

While true, wouldn't it follow that if you're not making full power, you won't need as much fuel for cooling either? I'm pretty sure the fuel to air ratios have been well thought out and tested for all power lever positions by some pretty smart engineers.
I think this is part of what hoptwoit is getting at.

[Ki-ll]

While true, wouldn't it follow that if you're not making full power, you won't need as much fuel for cooling either? I'm pretty sure the fuel to air ratios have been well thought out and tested for all power lever positions by some pretty smart engineers.
I think this is part of what hoptwoit is getting at.

The bigger issue here is that using partial power take offs in the Navajo is unsafe and also illegal since you have no idea what the actual power is and as far as I understand that's the point hoptwoit is getting at. I am onboard with that line of thinking. Whether the engineers tested this non-standard engine power I do not know, I would stay on the cautious side and set for that extra cooling fuel. I think it is very needed on that J2BD powerplant as it is working very hard.

[GyvAir]

I'm pretty sure we're of the same frame of mind here, if not exactly on the same page. I'm just saying that in reducing power by pulling back on the throttles, you're also proportionately reducing the need for that extra cooling fuel.

Looking at the photos on the TSB site though, I'd have to agree with a previous poster who suggested it may have been an altogether lack of fuel that led to this. Two wings torn off and both engines nearly dislodged, yet no fire or evidence of any precautionary foaming by emergency crews?

[Donald]

I'm pretty sure we're of the same frame of mind here, if not exactly on the same page. I'm just saying that in reducing power by pulling back on the throttles, you're also proportionately reducing the need for that extra cooling fuel

Are you sure it's proportional though?

IE if you pull the throttle back 2 inches (roughly 5%), are you getting a 5% reduction in fuel flow, or is the fuel flow reduction higher?

[GyvAir]

Honestly, I have no way of knowing that, one way or the other.
Is there a power setting range on the PA31 below max and above normal cruise that it's recommended not to run continuous in? If there isn't any such restriction stated, I'd like to think the system was engineered to provide fuel as required at all settings. Stranger things have been built though.

[cdnpilot77]

How did this thread about an accident prone operator turn to inappurtenant details of why de-rating an engine is bad or the workings of a turbo charger?

They had an accident, a bad one, where VERY fortunately, all the people who were along for ride are able to see the sun shine for at least another day.

[GyvAir]

That's quite the word!
Personally, I'm for allowing conversations to run organically. This one's gone a bit tangential, but still related and still reasonably respectful. And, it will likely come back on track. These are speculation threads by nature, after all. Everyone who has worked around Navajos has heard the suggestions and arguments about limiting manifold pressure, etc. to 'save' the engines and the obvious hazards such actions create. It's not unreasonable for someone to raise that particular speculation when a Navajo fails to make it back to the runway.

Yes, however it came to be in that situation, the 8 people on board that aircraft were very lucky to have walked away.

[anofly]

does anyone know for sure if there was fuel of any type on board when it crashed ? or spilled around the crash site. it is very strange to think they ran out of fuel on takeoff. It may be easier to understand if they had fuel on board but not selected the tanks properly or wrong type of fuel made it run like a bag of hammers...

[upintheair_]

I made sure to double check yesterday on take off what MP I'm producing. 47''. Party.

[CID]

If you treat this forum as a microcosm of our industry, we have pilots who don't know how to fly, maintainer who don't know how to maintain and regulators who don't know how to regulate. Let's hope these are in the minority.

[Inverted2]

I have a few hours in that plane. When did it go to Keystone? RIP XLO

[RatherBeFlying]

Partial power takeoffs on turbine engines is a very different kettle of fish than with piston engines.

Bottom line: You don't get detonation in a turbine. If you could play with the fuel controller, the worst consequence would be a flame out.

A piston engine on takeoff power needs extra gas for cooling. Insufficient cooling leads to nasty stuff such as burnt valves and holes in pistons.

[oldtimer]

So many posters wag on about manifold pressure and partial power take-offs but few actually get down to the nittey gritty. First off, the Airplane Flight Manual and any supplements are the pilots bible, anything else is just hearsay. The AFM is quite specific, 2575 RPM, full rich mixture and full throttle, limited to 5 minutes. If the airplane is equipped with the BLR vortex generators, as most 'Ho's are, there is a slight change in the maximum power setting for take-off. 2575 RPM, full throttle and full rich mixture which will develope 350 HP with no time limit. No mention at all about manifold pressure except to say 49"/hg is absolute maximum and 43 "hg is factory set to provide 350 HP at sea level under ISA. The rest is DENSITY. Varies with field elevation and ambient temperatures in order to supply the 350 HP required to meet the minimum performance for a Normal Category airplane as sitpulated in USA FAR 23 and CARS 523.
Take-off performance is two engine Accelerate - one engine stop, two engine take-off and climb to 50 ft AAE and two engine climb to a safe altitude. One engine inoperative performance is charted AFTER the airplane is configured for a OEI climb and the AFM is quite specific about what to do BEFORE the airplane is configured for a OEI climb, which it looks like the crew may have been attempting to do. Basically, if the airplane will not climb with gear or flaps down or propeller still windmilling and the aircraft is below 107 KIAS, look for something soft (and inexpensive) to land on.
Partial power take-offs is either a turbine engine thingee or some large engine manufacturers will chart lower power settings necessary with lower octane fuels so if you cannot get 115/145 octane fuel for your Bristol freighter or C 46, there are power charts to use. For a turbine, most operators will use an assumed temperature procedure. Basically, go to the NET TAKE-OFF FLIGHT PATH charts and see if you can meet flight path limitations at +35C or +40C and use those numbers when in fact the actual ambient temperatures are lower but that is only for airplanes with certified OEI take-off performance such as all jets, the King Air 300/350/1900 and airplanes designed to FAR25/CARS 525. CARS 604/702/703/704/705 are the rules under which the airplane has to be operated, nothing to do with the way airplane is designed.
That is my opinion.

[pelmet]

Partial power takeoffs on turbine engines is a very different kettle of fish than with piston engines.

Bottom line: You don't get detonation in a turbine. If you could play with the fuel controller, the worst consequence would be a flame out.

A piston engine on takeoff power needs extra gas for cooling. Insufficient cooling leads to nasty stuff such as burnt valves and holes in pistons.

That is my understanding. The last bit of power pour some extra fuel in for cooling.

[switchflicker]

Thanks Oldtimer. What you said makes perfect sense particularly "...First off, the Airplane Flight Manual and any supplements are the pilots bible, anything else is just hearsay..."

[Hetfield]

The crew obviously did a great job saving lives. I wish you guys speedy recoveries and a successful exit to a better employer. I was employed by this company for almost 2 years and was able to escape with my life, with no accidents and only memories of shouting matches with "the boss" when I turned down trips due to no alternate IFR pressures and fatigue. XLO will be missed; many good memories in that bird - It was all mine for a season in AB.

Cougarhunter, great post!!!!

The only thing I want to add to this thread is this: As PIC, it is your responsibility to make sure the fuel is the correct type and given in the correct amount. Early on in my career, I was taught to stay with the plane whenever someone outside of the crew was servicing it. I too have caught the fueler trying to put incorrect fuel into my AC except it was Avgas in a King Air. He pulled up in CYMM and I just said try again!!!!

Stay safe AVCanada-ers!!!

[SnotRocket]

No mention at all about manifold pressure except to say 49"/hg is absolute maximum and 43 "hg is factory set to provide 350 HP at sea level under ISA.

This is how the rumor that operators were de-rating their engines on the Navajo got started. Someone didn't actually read the AFM.

[GyvAir]

No rumor.
I've personally been admonished for refusing to limit a Chieftain to less than specified in the manual because “all the experienced operators do that to keep from blowing jugs”. As far as the nitty gritty of it goes, there’s enough years between me and any Navajo that I don’t remember the numbers and I’d have to read a bit before I would remember how you would go about improperly adusting it to get that inadvisable desired effect.

[cncpc]

No rumor.
I've personally been admonished for refusing to limit a Chieftain to less than specified in the manual because “all the experienced operators do that to keep from blowing jugs”. As far as the nitty gritty of it goes, there’s enough years between me and any Navajo that I don’t remember the numbers and I’d have to read a bit before I would remember how you would go about improperly adusting it to get that inadvisable desired effect.

Flat head screwdriver, apply and turn.

[FAF]

http://wwwapps.tc.gc.ca/Saf-Sec-Sur/2/c ... d2015C3475

Link to Cadors.

[digits_]

http://wwwapps.tc.gc.ca/Saf-Sec-Sur/2/c ... d2015C3475

Link to Cadors.

From which we can conclude:
- half a mile further and we wouldn't have heard a thing about it
- it is hard to loose count when you are rescueing people: 7 or 8, who cares. Or did one person mysteriously disappear to get the W&B legal ?
- it appears to be bloody hard to create a Cadors on which "Further Action Required:" is answered by "Yes". Even crashing your airplane with paying customers on board doesn't do the trick

[DanWEC]

From which we can conclude:
- half a mile further and we wouldn't have heard a thing about it
- it is hard to loose count when you are rescueing people: 7 or 8, who cares. Or did one person mysteriously disappear to get the W&B legal ?
- it appears to be bloody hard to create a Cadors on which "Further Action Required:" is answered by "Yes". Even crashing your airplane with paying customers on board doesn't do the trick

Not only that, but by the entry,

There were 8 soles on board and all were able to get out of the aircraft.

there were 4 people on board and all managed to escape with their shoes unscathed.

Jokes aside, any new info on the nature of the failure?