Density Altitude

AcroGimp

Cleared for Takeoff
Joined
Aug 30, 2013
Messages
1,480
Location
San Diego, CA
Display Name

Display name:
AcroGimp
When I took my mountain checkout in the flying club Bonanza, my instructor, another pilot and myself flew to Salida CO (KANK).

When we landed (field elevation 7523'), it was a little after Noon and it was reading 100 degrees on the tarmac. We broke out the AFM/POH, checked the TO performance chart in Section 5, and found that when plotting temperature vs altitude we could not interesect on the printed page.

Asked the instructor if we would be OK, he said he thought so, so the three of us trundled out to the trusty A-36, taxied out to the departure end of 06, took the active, put the coals to it, and slowly started down the runway (it was slightly downhill).

When we finally lifted off, about 5,000 feet down the 7,400 foot runway (I was literally about to abort the takeoff) it dawned on me, if you can't plot the DA and stay on the page of the AFM/POH, you ought not be flying.

We circle climbed to pattern altitude, on the stall horn, recovered, and had a very enlightening debrief. We then ate lunch, let it cool off a litttle, then flew with just one pilot and the instructor for both of us to get our 3 TO's/ldg's.

On our departure to return to Wichita, a glider pilot on the end of the runway notified us one of the main gear doors was hanging low, so we slowly made our way back to Beech Field. Later found out a previous pilot had oversped the gear and not reported it, which had, very slightly, contributed to the poor performance in the hot, high air at Salida.

We can't be afraid of learning, nor should we be afraid of sharing lessons learned - I have shared this experience with several flying friends over the years - it is good for some laughs but I believe had we been in a lesser plane my instructor would not have allowed us to try to takeoff as the result would have been disastrous. He is an ABS instructor and knows the Bonanza extremely well - he knew it could do it, and he knew we would learn an important lesson.

'Gimp
 
I hope you did learn. And signed up a new instructor. Among other things, he was teaching bad judgement and not teaching the importance of pre flighting. Or of density altitude.
 
DA not on the chart? Congrats, you are now a test pilot and outside the envelope at that. Have fun!
 
I hope you did learn. And signed up a new instructor. Among other things, he was teaching bad judgement and not teaching the importance of pre flighting. Or of density altitude.
FWIW, I understand where my instructor was coming from. He knew the plane could do it, but he also knew it would be uncomfortable. Certainly might not match up with your definition of a good instructor, and I can accept that, but it was a lesson that I will never forget - a truly visceral experience.

I believe it actually burned in the importance of preflight, and ADM, to a greater extent than all my prior training and experience - I am very serious about both preflight planning and ADM, and I personally credit this experience as a not-insignificant part of that. That said, your mileage may vary.

'Gimp
 
I hope you didn't take too much offense to my comments. I have read and enjoyed many of your posts, including this one for its educational value, and I have a lot of respect for you. But that CFI screwed up and it could have cost lives. There are probably a lot of headstones out there where the deceased would probably like to inscribe "I'll never do that again".

FWIW, I understand where my instructor was coming from. He knew the plane could do it, but he also knew it would be uncomfortable. Certainly might not match up with your definition of a good instructor, and I can accept that, but it was a lesson that I will never forget - a truly visceral experience.

I believe it actually burned in the importance of preflight, and ADM, to a greater extent than all my prior training and experience - I am very serious about both preflight planning and ADM, and I personally credit this experience as a not-insignificant part of that. That said, your mileage may vary.

'Gimp
 
I hope you didn't take too much offense to my comments. I have read and enjoyed many of your posts, including this one for its educational value, and I have a lot of respect for you. But that CFI screwed up and it could have cost lives. There are probably a lot of headstones out there where the deceased would probably like to inscribe "I'll never do that again".
No offense taken, it truly was a 'never again' experience. All I wanted was to expand a bit that my CFI really was a good guy, really did know the Bonanza (he was an ABS instructor), and would not have let us go were he not confident the plane would be OK - that said, any real issue with engine, systems, or significant wind change and it could have been ugly which is why preflight planning and ADM are so important - to prevent the ugly to the greatest extent possible.

I had maybe 170 TT at that point (12-13 years ago), had just finished my Instrument Rating and was checking out in the A-36 in advance of a planned trip to Vegas (great trip BTW).

'Gimp
 
I hope you didn't take too much offense to my comments. I have read and enjoyed many of your posts, including this one for its educational value, and I have a lot of respect for you. But that CFI screwed up and it could have cost lives. There are probably a lot of headstones out there where the deceased would probably like to inscribe "I'll never do that again".
The thing is that if people jump on posters who relate "never again" experiences, others will decline to reveal them and nobody will learn anything.

This is not specifically aimed at you, John, but is a common occurrence on the forums.
 
Last edited:
In experimentals you may not even have a DA chart in the POH.
 
Why were you "on the stall horn?" That would be way below Vy and most likely behind the power curve. No wonder you barely climbed.
 
Why were you "on the stall horn?" That would be way below Vy and most likely behind the power curve. No wonder you barely climbed.
Slight exaggeration for dramatic effect. We did take a while to accelerate (hanging main gear door unknown to us at the time), so more acurately, because it was slightly bumpy we would get occasional chirps on the stall horn - initially working for best angle due to terrain, so starting around 85 KIAS at first, then accelerated out to best rate of 100 KIAS - we were making about 300 fpm as I recall (going from memory).

'Gimp
 
I can relate. DA is one or those things that until you experience it, you may not fully respect it...or realize how scary it can be!

When you are taking off at a 5500' field in the middle of nowhere New Mexico on a hot day close to full gross and once you lift off your only two options appear to be the ground or stall horn...I also learned about the "pucker factor" that day!

In reality the numbers were fine but when you are used to shooting up at 800 FMP and you are only pulling out 200-300 FPM its an eye opener!
 
Good story. I have never been into Salida but flown over many times both GA and 'at work' and enjoyed the views getting into Denver... that reminds me of a density altitude story of my own in a fully loaded Piper Arrow (eek!!) out of Weed, CA one summer day. One of those things that leaves a memorable impression if you get out of it....
 
The thing is that if people jump on posters who relate "never again" experiences, others will decline to reveal them and nobody will learn anything.

This is not specifically aimed at you, John, but is a common occurrence on the forums.
Marie, I have been thinking about what you said and I learned a lesson here. You are right. I should not have diverted the tread to a rant about the instructor. It was a good and meaningful post and there are a lot of us that need to have the importance of density altitude drilled into us. Especially those of us that don't fly out of high altitude airports much.
 
Thanks for the post.just made a trip south from mass. Da was a factor on the trip from Atlanta south due to still high temps. I usually adjust fuel for flights according to high DA s.
 
Along the same "never again" lines, I was on about my 4th or 5th day after receiving my PPL and only thought I knew what I was doing. Took a couple buddies into Durango, CO in March for a snow skiing run, the arrival itself was bad enough and I nearly wrinkled a wingtip (turbulence, gusty winds, high DA, not enough power, poor planning, bad decision making etc etc), but that's a whole 'nuther story.

On the departure it was fairly warm and I was in a tired rental 172 right at max gross. I couldn't plot the DA but I knew the runway was 9200' long, so I figured if I wasn't airborne by the 3000' remaining sign I would abort. I burned about 5000', maybe 5500', before lifting off and was climbing out to the south (descending terrain) at about 150 a minute and that was all she had in her. I remember looking down from about 15 feet altitude watching the "3" sign disappear under the nose and thinking "uhmmm...."

The two guys that went with me on that trip still refer to it as "The Buddy Holly Flight."
 
Last edited:
Don't head up the valley to LXV, the DA at KANK was only 1600' above field elevation at Leadville...
 
Don't head up the valley to LXV, the DA at KANK was only 1600' above field elevation at Leadville...

Yup, a couple Saturdays ago I taxied about 4,000' before lifting off at LXV. I had been making fun of the other folks doing the same thing. I thought the turbo would give me a little more advantage than it did.
 
Yup, a couple Saturdays ago I taxied about 4,000' before lifting off at LXV. I had been making fun of the other folks doing the same thing. I thought the turbo would give me a little more advantage than it did.

Yup, turbo doesn't boost the wings at all.
 
Yup, turbo doesn't boost the wings at all.

Or prop,

I ate a good portion of the runway on my first departure there, AWOS said "density altitude one three thousand"

Most recent trip there we left a bit earlier in the morning:yes:
 
I can relate. DA is one or those things that until you experience it, you may not fully respect it...or realize how scary it can be!

When you are taking off at a 5500' field in the middle of nowhere New Mexico on a hot day close to full gross and once you lift off your only two options appear to be the ground or stall horn...I also learned about the "pucker factor" that day!

In reality the numbers were fine but when you are used to shooting up at 800 FMP and you are only pulling out 200-300 FPM its an eye opener!

We had a guy in our club panic and try to land the plane (182) after getting scared by poor DA performance. At least thats what some people think - not sure we'll ever know the real story. Nearly totaled the thing...
 
We had a guy in our club panic and try to land the plane (182) after getting scared by poor DA performance. At least thats what some people think - not sure we'll ever know the real story. Nearly totaled the thing...

A poorly flying airplane is still a flying airplane - no sense stuffing it in the ground as long as it's still flying...
 
Yup, turbo doesn't boost the wings at all.

Two problems at LXV that day.

One was that I topped off with cheap gas which I had never done there before. I have climbed out of LXV on a July day at 1,000 fpm when I'd burned off a coupe hours of fuel getting there and didn't fill it up. In other words, I was heavier than when I had been in there previously.

The other was a direct crosswind. We don't think about it much usually but a direct crosswind does cause some airflow problems on ground roll and a bit more drag since we're holding aileron into the wind.

With the turbo I had full engine power compared to all the NA guys who lost more than 20% of rated power. The constant speed prop isn't much of an issue - see http://www.nar-associates.com/technical-flying/propeller/takeoff_propeller_efficiency_screen.pdf for a discussion that indicates very little effect on propellor efficiency with changes in DA.
 
Two problems at LXV that day.

One was that I topped off with cheap gas which I had never done there before. I have climbed out of LXV on a July day at 1,000 fpm when I'd burned off a coupe hours of fuel getting there and didn't fill it up. In other words, I was heavier than when I had been in there previously.

The other was a direct crosswind. We don't think about it much usually but a direct crosswind does cause some airflow problems on ground roll and a bit more drag since we're holding aileron into the wind.
You also had about 115 lbs. of extra dead weight, maybe 120 with the pancakes and orange juice. At least I didn't get the feeling that I wanted to pick my feet up at the end of the runway as I have at other times in my life.
 
You also had about 115 lbs. of extra dead weight, maybe 120 with the pancakes and orange juice. At least I didn't get the feeling that I wanted to pick my feet up at the end of the runway as I have at other times in my life.

Protest! wasn't dead weight, was self loading weight...
 
Good story.

Both of my mountain instructors give out those " off the chart " scenarios and then discuss both extrapolation using math, and whether or not it's a good idea in your aircraft. They don't ascribe to the " test pilot " concerns too much or there's some POHs that would leave many aircraft grounded up there if you had to be on the chart. It's also important to know to what degree you're off the chart since there's some limited margin for climb rate right near the edge.

Both tended to advise Extreme caution in the mountains whenever any high airport was over 75F. 100F is really pushing it up there. Frankly knowing what I know, 100F and three people is likely a solid no-go in my normally-aspirated 182.

The other thing they stress is setting a hard go/stop point and aborting if that point on the runway goes by, no matter what. 5000' down the 7000' runway is not the time to be deciding. Decide where you'll abort before the power comes up.

These concepts are everyday normal procedures for professionals. Private pilots would do well to build a Take Off and Landing Data sheet (TOLD) and fill it out for every flight if using dissimilar aircraft in the rental fleet, and if flying the same aircraft all the time, getting it out below certain pre-calculated numbers for runway length or high DA. DA around here should be calculated for every takeoff, or known within at least 500' by experience.

Glad you guys made it. At least if you can keep it flying there's lower terrain South of Salida. It's your only "out" there. And there's room to make a wide shallow turn in the valley. Going up-valley to LXV in your scenario would be... not advisable. ;)

Clark's LXV story is pretty common there too regarding cross-winds. The line of pine trees off to the side does bad things to the air there when it's a crosswind. You'd think it'd act as a windbreak but it really seems to just make things messier there instead.
 
Glad you guys made it. At least if you can keep it flying there's lower terrain South of Salida. It's your only "out" there. And there's room to make a wide shallow turn in the valley. Going up-valley to LXV in your scenario would be... not advisable. ;)
I think you are imagining something worse than it was.
 
I believe the instructor did the perfect scenario, got your attention, without being too dangerous. The counterpoint is that if you would have taken off light or in cooler temps the effect would not be so dramatic and you might discount it as an over blown concern. I'm sure you'll be careful with DA for the rest of your flying career. How could there be a better lesson.

I have flown several otherwise capable aircraft in the mountains and experienced a lot of DA effect, it sure got my attention a couple of times also. That's one big reason I bought my 206. It allows me to take off from 7K, 100 degrees, 4 up, full fuel, no drama.
 
Good story.

Both of my mountain instructors give out those " off the chart " scenarios and then discuss both extrapolation using math, and whether or not it's a good idea in your aircraft. They don't ascribe to the " test pilot " concerns too much or there's some POHs that would leave many aircraft grounded up there if you had to be on the chart.

I don't know about other mfgs but being a Bonanza, the chart represents what has been demonstrated in actual conditions. If the parameters were not in the charted region, then Beech did not demonstrate in that region, and they were, despite the hyperbole in the test pilot region. I've done the same in xwind take offs where I was at the edge of the chart based on conditions, and it was a SOB to hold the plane down the runway.

Also, no pre-flight actions can detect a gear overspeed condition with the exception of actual bent fairing metal. If that were the case, it's also quite hard sometimes to detect. I'm guessing the gear retracted fully into the wells, and the gear up light was on, but they had fairing metal that was not fully seated causing drag. As the OP learned, this is very hard to detect in a Bonanza, unless the fairing is a pretty big one. One of the primary telltale signs is the skid/slip ball for main gear faults, as the main gears are quite wide, and will skew the plane if left hanging. Of course, if both are hanging, you won't get any skid/slip indication and that happens to the inner gear doors most often.
 
Doesn't Leadville (LXV) have an unofficial "suggestion" that if the temp is 85+, no ops are allowed for little airplanes?
 
I don't know, but 85+ would be really hot for Leadville. Does it ever get that hot?
 
Nate's point about having an abort point is spot on, as is knowing your "outs" Saliada is nice as its location means that you have slightly lower terrain around. Pitch for VY and fly away from the rocks
 
Nate's point about having an abort point is spot on, as is knowing your "outs" Saliada is nice as its location means that you have slightly lower terrain around. Pitch for VY and fly away from the rocks

Pitch for Vy at ALTITUDE. Climb performance can really suck if you pitch for sea level Vy at high density altitude. The difference is not small.

I learned this the somewhat hard way in a Warrior at Big Bear (with an instructor). 75 is much too fast. 65 works real nice.

I thoroughly agree on the abort point. I make that part of my preflight planning routinely.

At South Lake Tahoe, I determined that I should be at 50 feet well prior to 4000 feet on a 90 deg day. That's roughly near the tower, and 50 feet makes sense for that particular airport because that's a long runway -- there is still 4500 feet remaining after that. When I tried it on an 85 deg day, climb performance was real sluggish as one might expect, but I was well above 50 feet by the tower and still climbing slowly, so I went on.
 
Last edited:
I don't know about other mfgs but being a Bonanza, the chart represents what has been demonstrated in actual conditions. If the parameters were not in the charted region, then Beech did not demonstrate in that region, and they were, despite the hyperbole in the test pilot region. I've done the same in xwind take offs where I was at the edge of the chart based on conditions, and it was a SOB to hold the plane down the runway.

Also, no pre-flight actions can detect a gear overspeed condition with the exception of actual bent fairing metal. If that were the case, it's also quite hard sometimes to detect. I'm guessing the gear retracted fully into the wells, and the gear up light was on, but they had fairing metal that was not fully seated causing drag. As the OP learned, this is very hard to detect in a Bonanza, unless the fairing is a pretty big one. One of the primary telltale signs is the skid/slip ball for main gear faults, as the main gears are quite wide, and will skew the plane if left hanging. Of course, if both are hanging, you won't get any skid/slip indication and that happens to the inner gear doors most often.
It was the right inner gear door, it appeared closed during preflight but the effect of propwash/relative wind was sucking it open - the glider pilot reported it was enough for him to see when we flew overhead (he was positioning for a tow). It did not, as I recall, require me to carry additional rudder on the flight out, but with the YD and Autopilot on I would not likely have noticed, when I killed the A/P and YD it was bumpy enough and I was setting up for approach/landing my feet would have been busy.

When the plane was examined after we got back to Beech, we found that the hinges were bent indicating an overspeed and a quick review with the pilots who flew her before we did found the culprit.

'Gimp
 
Doesn't Leadville (LXV) have an unofficial "suggestion" that if the temp is 85+, no ops are allowed for little airplanes?

CPA cut-off for their flying portion of their training for the instructors using their "name" is 75F at KLXV.
 
I think you are imagining something worse than it was.

Not sure what you mean... at Salida, if you're airborne and missed the obstructions around the airport, you're pretty much okay unless you start yanking and banking while slow... just go south and the terrain will slowly drop as you also burn off fuel. That's an "OMG" worst-case scenario there... which really is not much of a big deal in that portion of the valley.

There's far more entertaining mountain airports than Salida... as you and I both know. :)

Flatlanders still get their eyeballs puckered at the lack of performance at Salida though, on a nice toasty day. :) It's one thing to see it in the POH book, it's another to experience it first-hand.

I have the opposite problem at sea-level... my eyeballs pucker at the climb rate of the 182 down there. Heh... I always feel like I should be pushing the nose down and climbing faster... then I look at the ASI and think, "man, that's cool..." :)
 
You said you were glad we made it and there was not even a question, at least in my mind.

Oh yee of great faith - don't you know that the engine could have stalled at any second? We were lucky not to make a smoking hole I say, lucky. I pulled that aircraft into the sky by shear strength, strength alone. If I'd even changed one thing we'd still be there, maybe in pieces, but still there. :rofl::rofl:
 
Old Thread: Hello . There have been no replies in this thread for 365 days.
Content in this thread may no longer be relevant.
Perhaps it would be better to start a new thread instead.
Back
Top