Bravo Operations at High Altitude Airports

[PDXBravo]

After landing at an airport (KPNA) with a field elevation of 7,000 ft., the engine stopped immediately after I pulled off the runway to the taxiway. I thought maybe having the mixture full rich and the boost pump on (both checklist items for landing from the POH) at that altitude over enriched the mixture.  How do you alter, if at all, your operations when landing or departing a high elevation airport? 

[carusoam]

A couple of things are going on at the same time...

At low power settings, the turbine is slowing down... causing even lower power settings....

You may want to read-up on airborne engine restarts with a failed turbo...

Expect pulling the mixture back should help keep things going...

Are you familiar with the restart procedure with the failed turbo?  There is an altitude that needs to be achieved (descending) to make it work....  7k’ is pretty close to that altitude....

Pp thoughts only, stuff I read about on MS... I don’t have the first hand TC experience...

Best regards,

-a-

[jlunseth]

I don’t know what the Bravo altitude is, the 231 POH says 12k. But the altitude is published because above 12k without a turbo, there just is not enough air for the engine to run.  That is not what is happening on the ground even at 7k.  I don’t think he is in danger of an airstart though.  The engine shuts down after landing because the aircraft is no longer moving fast enough for the prop to help the engine.  In the air, where airspeed is much higher, there is much more latitude in terms of mixture control.  You can be much richer or much leaner than at idle on the ground, and the engine will operate just fine.

My guess is that you were overrich, you might want to think about turning the boost pump off as soon as you touch down.

Also, the POH may say you should be full rich for landing, but in my 231 I have found that causes the engine to burble from being overrich.  The POH wants the engine full rich in case you must go around, but for me, it is just as easy to land with the engine leaned out some, and if I have to go around I push the mixture in.  

[carusoam]

Jl = My goto guy for great technical writing regarding turbo Mooney ops! 

Thanks Jl!

Best rgeards,

-a-

[midlifeflyer]

No experience with the Bravo, but plenty with other turbos in high altitude ops. Like any other turbo, 

Mixture...FULL RICH (on final)
like its twin
Propeller... HIGH RPM (on final)

in the Bravo POH is in anticipation of a go-around so you get the benefit of the turbo boost. "On final" is a short enough time (in theory anyway) to avoid the downside of full rich ops. But, although the POH doesn't say so, he next step after you touch down is to lean the mixture for ground ops, even if it's just a guestimate.

Personally, I treated it differently the 20 years I lived in Colorado (at least once I knew what I was doing). POH notwithstanding, in the turbos I flew, SOP was to remain leaned for landing, with mixture full rich exclusively being part of the go-around procedure.

 

 

Edited August 2, 2018 by midlifeflyer

[PaulM]

I have seen a similar problem at 6K (KPUC) in Utah on a hot day last year in my Bravo,   The engine didn't stop after landing, but on restart I had to run it lean on the ground until ready for takeoff.

Here is the problem, turbo'd planes want full rich, when the turbo is generating 34".... but that is way too rich at altitude when you are idling and the turbo isn't spooled up.   

So,

  now we discuss best practices.    For start and takeoff you start somewhat leaner than full, whatever is necessary to keep it running... then on takeoff once the turbo is spooled up, you switch it to full rich. 

2 hours ago, midlifeflyer said:

Personally, I treated it differently the 20 years I lived in Colorado (at least once I knew what I was doing). POH notwithstanding, in the turbos I flew, SOP was to remain leaned for landing, with mixture full rich exclusively being part of the go-around procedure.

And that seems to be what is needed for landing.   You shouldn't go full rich until you are on the go-around.... The plane will fly fine kept at the cruise/descent lean point, it just won't have the full cooling in the go-around of full rich but you will have full power.   

[midlifeflyer]

4 minutes ago, PaulM said:

I have seen a similar problem at 6K (KPUC) in Utah on a hot day last year in my Bravo,   The engine didn't stop after landing, but on restart I had to run it lean on the ground until ready for takeoff.

Here is the problem, turbo'd planes want full rich, when the turbo is generating 34".... but that is way too rich at altitude when you are idling and the turbo isn't spooled up.   

So,

  now we discuss best practices.    For start and takeoff you start somewhat leaner than full, whatever is necessary to keep it running... then on takeoff once the turbo is spooled up, you switch it to full rich. 

And that seems to be what is needed for landing.   You shouldn't go full rich until you are on the go-around.... The plane will fly fine kept at the cruise/descent lean point, it just won't have the full cooling in the go-around of full rich but you will have full power.   

We do need to bear in mind, though,  that "full power" means "available power." At high density altitudes, without the turbo-boost, that's going to be significantly less than normally aspirated full power at sea level. There is also the potential problem of being too lean. That exists with normally aspirated engines but is exacerbated by the turbo "stuffing" more air into the system (hot dog eating contest is my mental image of a turbo) . Those are definitely handleable if one knows what one is doing, but can be a real problem if one doesn't anticipate what the high density altitude can do to all aspects of engine and aircraft performance.

[PaulM]

3 hours ago, midlifeflyer said:

e do need to bear in mind, though,  that "full power" means "available power." At high density altitudes, without the turbo-boost, that's going to be significantly less than normally aspirated full power at sea level. There is also the potential problem of being too lean. That exists with normally aspirated engines but is exacerbated by the turbo "stuffing" more air into the system (hot dog eating contest is my mental image of a turbo) . Those are definitely handleable if one knows what one is doing, but can be a real problem if one doesn't anticipate what the high density altitude can do to all aspects of engine and aircraft performance.

Full power means the available power with the turbo...  What this means is that we need to have the MP first  (231's know that the MP is a limit you can exceed) ... and then the mixture to match it... With the turbo at idle we are a normally aspirated engine and need to be lean at altitude to idle.   

the problem is that the Boost pump + max rich is set for sea level operations and at a high density altitude it is too rich for idle operations.   We aren't too lean.. we are too rich... so you land "leaned"... and then don't take off or go around until you have the MP first..  Then to the fuel injector, it is a 34"  ISA takeoff.  

I have only seen this problem at 6K + 90F.  and a hot restart.... 6K +90.. 1st start didn't require any leaning.    I suspect that this is near the limit. 

[BuzzProc]

My $.02 is the following.  To a degree, it isn't that surprising your engine quit, more like it drowned in fuel.  Happened to me once in a Bravo I owned for two years.  I live at a 5000' airport and have often landed at higher than 7000'.   In my landing check, I do put in full mixture, unless we are talking Leadville but I never put the boost pump on.  Just didn't and doesn't make sense to me.  Particularly in a Bravo.  If you have the boost pump in so you can perform an emergency Go around, well in the Bravo, putting in full power turns on the boost pump anyway.  So you get it when you need it, but not, when you don't.

As the other gentlemen said, I am leaning before I even turn off the active.  Aggressive leaning is important at any altitude.

JP

[carqwik]

+1 on aggressive leaning for the Bravo (on the ground that is).  I also do not turn on the boost pump for landing...   As for approach, I enrichen the mixture but don't go full rich. 

[HXG]

In my Bravo in Colorado, I remain aggressively leaned for all ground ops. I don’t advance the mixture full rich on final. I usually leave the mixture where it’s set or occasionally advance it some for a possible missed approach.  Of course, prop is  full in on final.

Most are taught to advance the mixture full rich for final on turbos. This is fine since it simplifies things, but I would lean aggressively on roll out at high DA airports to avoid an engine quit while  exiting the runway.  

Personally, I am spring loaded (and proficient/practiced) to immediately advance mixture full rich, throttle full, flaps 1/2, gear up, trim down physically with the trim wheel, while applying significant right rudder for a go around. 

[HXG]

I forgot to mention that I don’t land with the boost pump on. The boost pump switch on (and switch tanks) is another spring loaded action I’m always ready for.

[midlifeflyer]

18 hours ago, PaulM said:

Full power means the available power with the turbo...  What this means is that we need to have the MP first  (231's know that the MP is a limit you can exceed) ... and then the mixture to match it... With the turbo at idle we are a normally aspirated engine and need to be lean at altitude to idle.   

the problem is that the Boost pump + max rich is set for sea level operations and at a high density altitude it is too rich for idle operations.   We aren't too lean.. we are too rich... so you land "leaned"... and then don't take off or go around until you have the MP first..  Then to the fuel injector, it is a 34"  ISA takeoff.  

I have only seen this problem at 6K + 90F.  and a hot restart.... 6K +90.. 1st start didn't require any leaning.    I suspect that this is near the limit. 

Agreed. I think we are saying the same thing. If you don't do the "mixture to match it" you are going to have issues. Plus, it always helps to bear in mind that density altitude affects more than just engine performance.

[FoxMike]

Have been operating a Bravo for 15 years.  Taxi with mixture lean.  As you pul into position on runway mixture goes full rich.  On final I always have the engine at less than full rich and do not use the fuel pump.  Hint if you ever needed to use full power for a go around you would be so far out of trim that would stand a good chance of stalling the airplane.  If you need to go around use partial power until you get the trim set.  The airplane will do a fine go around on part throttle.

[jlunseth]

Me too on the go around.  I don’t put all the power in right away.  The most important thing is to get the aircraft properly trimmed up and the fuel flow setting correct before putting in full power. I guess I don’t even think about it, I just put in partial power to keep me level above the runway until I get everything set up.

Now, if I ever found myself about to settle down on the belly because I forgot the gear, I would probably react differently! But a normal go around, control is most important.

[HXG]

Agree with the word of caution on the go around especially if you’re near the runway and  trimmed for landing since the Bravo and Acclaim pitch up dramatically with sudden full power.  I advance the power smoothly but don’t get to full power until I get that trim wheel rolled forward agreessively with my right hand (forget the thumb electric trim button- it’s too slow to keep up with trim needed). 

[PDXBravo]

Very helpful.  I suspected that boost pump off/keep lean was the answer but it's helpful to learn from other experience.  Thanks gents.  

[thinwing]

Aggressive leaning on ground...if not sure how much ,try 11/12 "turns"of the wrist on the vernial mixture,i.e. About 1/3 a revolution per turn.Count to 11 or 12 

[PDXBravo]

This morning:  "Telluride traffic (9078 MSL) Mooney 10KG departing runway 27", then lights, transponder, mixture full rich and.... the engine promptly died.  Started back up, leaned for max power at 2000 RPM, taxied on to the runway, applied full power THEN went full rich.  Worked like a charm, 1000fpm climb out.

So many things the POH doesn't explain you must learn...

[carusoam]

How was the skiing?

https://tellurideairport.com

-a-

[Davidv]

On 8/3/2018 at 10:56 PM, FoxMike said:

Have been operating a Bravo for 15 years.  Taxi with mixture lean.  As you pul into position on runway mixture goes full rich.  On final I always have the engine at less than full rich and do not use the fuel pump.  Hint if you ever needed to use full power for a go around you would be so far out of trim that would stand a good chance of stalling the airplane.  If you need to go around use partial power until you get the trim set.  The airplane will do a fine go around on part throttle.

This is exactly how I fly mine too.

[alextstone]

10 hours ago, PDXBravo said:

This morning:  "Telluride traffic (9078 MSL) Mooney 10KG departing runway 27", then lights, transponder, mixture full rich and.... the engine promptly died.  Started back up, leaned for max power at 2000 RPM, taxied on to the runway, applied full power THEN went full rich.  Worked like a charm, 1000fpm climb out.

So many things the POH doesn't explain you must learn...

@PDXBravo, my wife and I are headed to Telluride Thursday...thanks for the tip!

[PDXBravo]

9 hours ago, carusoam said:

How was the skiing?

https://tellurideairport.com

-a-

@carusoam Perfect conditions.  3 days skiing back to back, open to close.  For all the heavy metal on the ramp, KTEX is surprisingly GA friendly.  Reasonable tie down, hangar, and fuel prices.