L35: Mtn Flyn for n00bs

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jFlight

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http://www.pilotsofamerica.com/forum/showpost.php?p=982835&postcount=12

New post to not derail another thread.

craigvince said:
Don't kid yourself. That's a very dangerous airport. At that altitude, a C172 with 2 people in it can be dicey climbing out. I don't mean to offend, but your statement alone indicates you need mountain flying training.
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You could suppose that based upon student pilot status with zero mountain training alone...

But in seriousness...

Through beginning of August...lowest pressure I could find at L35 about midday was 30.15" Hg... this is factoring pressure altitude in your favor: assume runway elevation equals pressure altitude...round up to 7k' (more conservatism). Now let's assume an extreme factor of the hottest L35 temperature experienced in years...32 deg C. Round to 30 to make it easy in the POH for example sake...

Short field TO at 2300lb max gross is 3,245'. L35 runway is 5,580'. Check.

Move up to 9.5k' pressure altitude for safe entry clearance into BB valley from the west. At max gross...we run into trouble according to the POH. I wouldn't try it. By the POH, if temp was 68 deg F, at 10k pressure altitude, there is 230fpm climb available. If I was at max gross, if I absolutely had to, I'd go for it if temps were 68-70F. I know you can snake out of the west end at a little less than 9.5k' MSL.

So, down to only two passengers, probably something around 1900lbs gross... it looks like temps closer to 78+F and/or exceptionally low barometric pressure would cause potential concerns. But 78+F at BB happens only on the hottest of the hot days.

Now, again, I am a student pilot, endorsed to fly into L35. What I would check for is pressure altitude and temperature to determine adequate climb performance to enter/exit into BB Valley. The runway is adequate for pretty much all conditions to at least get off the ground. My initial statement was a quick drive-by thought...Incomplete for performance analysis to ensure safe BB Valley ingress and egress.

For sake of learning and safety, what else should I know? Something more specific than my need for mountain training...


http://www.pilotsofamerica.com/forum/showpost.php?p=982877&postcount=13

Palmpilot said:
Amen. I took off from there in a fully loaded 172 last July, and if there had been significant downdrafts my goose would have been cooked. As it was, it was obvious after takeoff that I needed to follow the advice on the sign about where to do my climbout.
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I thought of downdrafts, too... Would this be potentially more significant existing from the east side of the valley?
 
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Wind, which side of which ridge would help, what side would hurt, go/no go point, run the numbers.

Big Bear aint a hard airport to fly out of, but it's not some 10000' sea level strip ether .
 
The fact that you've done this much homework on the subject tells me your flight instructor is doing his/her job very well. You'd be amazed how many student pilots or new pilots fly up to Lake Tahoe (I'm in NorCal) and can't get out in the summer. And that airport isn't as high as BB. I'm really glad to hear more instructors take this subject as seriously as yours. :)
 
you keep referencing "pressure altitude" do you mean "density altitude"? Pressure altitude and density altitude are two different things. Density altitude at these airports in the summer can get way up there.
 
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Mixing up Pressure Altitude and Density Altitude.

Pressure altitude is whatever your sensitive altimeter reads when set for 29.92. No matter if you're on the ground, in the air, doesn't matter.

Density Altitude is Pressure Altitude corrected for non-standard temperature.

So you're correct, if you're aloft and the temperature is higher than standard for that altitude, performance drops off to whatever the DA is up there, just like on the ground.

And you're wise to take note of it when looking at obstacle clearances and significantly reduced climb rates aloft.

Altimeter settings are corrected for non-standard real pressure so that at the station on the ground, the altimeter reads the true height above sea level. Thus, the correction for non-standard pressure and non-standard temperature is "baked in" and would have to be reverse calculated to remove it to get the real air pressure at the surface.

Additionally your body also agrees with the airplane. Just because the altimeter says you're below the legal requirement altitude for O2 use, doesn't mean the partial pressure of air at your particular height above ground is safe. The altimeter says how high you are not what the airplane or your body are experiencing in real pressure.
 
jFlight said:
For sake of learning and safety, what else should I know? Something more specific than my need for mountain training...
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It sounds like you're doing okay for where you are in training.

Things to know: density altitude, mountain winds and the associated rules of thumb for light aircraft in those winds, leaning for max performance, the so called "visual precision approach," mountain weather in general and pass clearance requirements.

There's plenty more to learn - well beyond what I listed. Just some things to work on if you're flying around tall hills.
 
JBrown243 said:
you keep referencing "pressure altitude" do you mean "density altitude"? Pressure altitude and density altitude are two different things. Density altitude at these airports in the summer can get way up there.
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I think he has it right, he references the temperature in conjunction with the pressure altitude. While we often say density altitude and it produces a good mental picture of what the problem is, it turns out knowing the density altitude seldom really does us any good since few performance charts actually use density altitude. So he is saying it the way his performance charts work, look up the pressure altitude and move over to the temperature to get the performance for those conditions.

Brian
CFIIG/ASEL
 
Having recently climbed out of Big Bear at near max gross with a full plane (a 182), at DA of merely (for a 182) 10K, and needing almost the entire mile of that strip to establish a positive rate of climb... all I can say is, the book is one thing, actually doing it is another. The book assumes a perfect pilot, too, which I am not.
 
There's still more to mountain flying that calculating takeoff performance. A goodly number of the mountain crashes involve people who departed from lower altitudes.
 
No offense, onwards, but weren't you the guy that tried that climbout full rich? That's going to make a lot of difference.
 
MAKG1 said:
No offense, onwards, but weren't you the guy that tried that climbout full rich? That's going to make a lot of difference.
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Yeah :D like I said, I'm not a perfect pilot :mad2:
 
Big Bear has the cheapest gas in So Cal. Go figure. Filler up:confused:
 
1) Downdrafts at L35 can be unpredictable due to swirling winds in the "bowl".
2) Performance charts assume you have a nearly perfect mixture setting, which is difficult to achieve with typical GA aircraft instrumentation, and a best power setting may not yield sufficient fuel flow for adequate cylinder cooling. Getting off the runway is one thing, not going swimming in the lake is another.

Sounds like you have a good instructor and are a good student. Keep it up!

Jeff
 
The OP keeps referencing the POH - and that's the correct place to look for your aircrafts performance data - but keep in mind that the POH was written based on the performance of a FACTORY NEW airplane in perfect shape, with highly trained professional test pilots at the controls to get the absolute best performance out of the aircraft.

If you are not a perfect pilot flying a perfect airplane, you won't get that performance.

The POH is theoretical. Actual performance my vary drastically based on a number of factors. Give yourself some margin.
 
airguy said:
The OP keeps referencing the POH - and that's the correct place to look for your aircrafts performance data - but keep in mind that the POH was written based on the performance of a FACTORY NEW airplane in perfect shape, with highly trained professional test pilots at the controls to get the absolute best performance out of the aircraft.

If you are not a perfect pilot flying a perfect airplane, you won't get that performance.

The POH is theoretical. Actual performance my vary drastically based on a number of factors. Give yourself some margin.
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Good point. Surface condition plays a big part as well. We are talking about hard surfaced runways here but POH numbers won't work so well from a soggy mountain grass strip.
 
brcase said:
I think he has it right, he references the temperature in conjunction with the pressure altitude. While we often say density altitude and it produces a good mental picture of what the problem is, it turns out knowing the density altitude seldom really does us any good since few performance charts actually use density altitude. So he is saying it the way his performance charts work, look up the pressure altitude and move over to the temperature to get the performance for those conditions.

Brian
CFIIG/ASEL
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He has density altitude on the performance charts, it's at standard atmospheric temperature for the particular altitude. It's quite useful since we just have to know performance for specific altitudes. I hope that comes across as I meant it...it seems just a bit awkward on the phrasing.
 
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airguy said:
The POH is theoretical. Actual performance my vary drastically based on a number of factors. Give yourself some margin.
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One should always have an out, including aborted takeoffs and the usual 50% runway margin.

But if your performance differs drastically from the POH, you have an issue that needs to get looked at. I insist on near-book numbers from aircraft I'll bet my life on. And yes, that's realistic even on a 30+ year old aircraft. There will be some performance loss, but if you can describe it as drastic, you have an airworthiness problem. Or else you're doing something really wrong like not leaning or flying in a slip or flying at sea level V-speeds.
 
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jFlight said:
I thought of downdrafts, too... Would this be potentially more significant existing from the east side of the valley?
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It depends on the direction of the wind. When you're on the lee side of a ridge (i.e., the wind is coming from the other side of the ridge), then you can expect downdrafts near the ridge. The strength of the downdrafts will depend on the wind speed and on how quickly the terrain falls away.
 
Cool, that was my understanding with the winds. I asked about it being of greater potential on the east side as I believe the prevailing winds are from the southwest.

I also understand about margins. In my example above, my assumptions were conservative, including barometric pressure for the past month, which allowed the assumption that true altitude could be assumed to be pressure altitude. Pressure altitude along with temperature allowed me to pull the performance figures from the POH.

I know there's plenty more to learn, but I'm glad to see that I am not off base with the first steps.

Reason is that my CFIs have taught me very little. I had one that took me up to solo, whereupon he took a salary gig flying C206s for a photog company. And a second take me up to where I am at now. I have always been an effective independent and self-studier, and my CFIs have picked up on this immediately. So they have been relaxed and completely hands-off with the knowledge. I know the risk...they may not realize I didn't pick something up that I should have. I'm doing my best to not allow that.
 
jFlight said:
Reason is that my CFIs have taught me very little. I had one that took me up to solo, whereupon he took a salary gig flying C206s for a photog company. And a second take me up to where I am at now. I have always been an effective independent and self-studier, and my CFIs have picked up on this immediately. So they have been relaxed and completely hands-off with the knowledge. I know the risk...they may not realize I didn't pick something up that I should have. I'm doing my best to not allow that.
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Most (not all, to be sure) CFI's that I run across these days doing initial training don't have their heart in it anymore, they are building time looking for that next commercial job. Even then, they are only teaching the students the bare minimum according to the syllabus and the FAA requirements. That's a far cry from being a competent pilot, it's just a start - very similar to a 16-year with a fresh drivers license. It doesn't mean you are ready for Dallas rush-hour traffic. Never stop learning, and never assume you know it all.
 
Yeah, your understanding seems quite reasonable. I'd suggest taking an instructor for the first time and just going up there. There are a few things you'll need to do differently, such as never going full rich, leaning at run-up (and for engine start!), flying a slower Vy and a wider than usual pattern, checking surface wind forecasts at the peaks (graphical.weather.gov is a good source -- there are no aviation sources that provide this data for more than a few specific passes) and actual conditions at the airport, and so on.

You don't need to use your regular CFI. Find one experienced in mountain flying; there are quite a number, and your chief instructor may have a lead or two in your area.

It might be best to finish your private first, but that's a judgment call for you to make.
 
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I took one dual flight up to L35. My first solo xc was also to L35. I can't wait to take a leisure flight up there to park and hang out for a bit!

My flight plan for my checkride includes L35! Ha! Found that out today.

I am at a 141 school, catering to international students. Half of them don't even take their training too seriously, and are playing on their parents money. My first CFI, was a brand new CFI. Brand new to the U.S., via Italy, just coming out of the air force as a navigator. He doesn't seem to have any aspiration for airliners. Can't blame him for taking a salary gig buzzing around in photog 206s all around the country! My current CFI is 24; went to college for flying. He's had at least a couple different jobs, including charter around Havasu, but he is now back at home just kicking it with no responsibilities...partying it up before he decides to get serious. He'll have more than enough resume for when he decides to look for a more career oriented job.
 
jFlight said:
I am at a 141 school, catering to international students.
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Do yourself a favor and find an independent instructor who teaches because they love to teach and take at least one lesson, even if it's all outside of your 141 stuff and on your own dime.

You'll experience a very different world.

(You may not want to go back to the 141 school, either. But I understand if you're doing it on student loans and need the 141.)
 
Whoops...need to clarify... I am a part 61 student at the part 61/141 school that is predominantly 141 oriented.

Chose it because it's less than 6 miles from my pad and they have the lowest wet rate for a C172 around.
 
jFlight said:
Whoops...need to clarify... I am a part 61 student at the part 61/141 school that is predominantly 141 oriented.

Chose it because it's less than 6 miles from my pad and they have the lowest wet rate for a C172 around.
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Finally! Someone who knows how to spell "predominantly"!
 
Different strokes for different folks.
 
Well, you SoCal people who want to fly into Big Bear, but haven't yet, have a new resource.

Apparently, Mend Aviation at Whiteman/Van Nuys is having a free seminar on just how to do that, tomorrow (15 Sept) at 9AM.
 
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