Density altitude and runway length quick guide?

[flyingcheesehead]

Make sure I’m on same page- I understand what you say on rollout but distance is time too so I wasn’t thinking of landing roll as much as rounding out or if you are on final and ya notice your sink rate is greater than you would like it’s going to take more time and distance when you add the power in to arrest that sink rate won’t it? So you would want to make sure you don’t find yourself short as what normally could be solved with a touch of power may take a more dramatic touch of power if you misestimated initially, right or no?

Well, you're already going to be short of power up there, so to some extent, yes. However, not much really changes. Distances in the forward direction are going to go by faster, but the plane will feel the same (same IAS) and you'll just notice your groundspeed is faster than normal.

The airplane is going to sink faster than normal just as it will climb slower than normal correct?

If you're maintaining a 3-degree glidepath, and the same airspeed (which you should be), your true airspeed will be faster and thus your descent rate will also increase a little - Not a lot.

So speeds should be kept the same but power setting at home (moderate temps at 800ft) May be lower than what you use in high DA to accomplish same indicates airspeed and sink rate in the pattern?

If you have a constant speed prop, no. Your throttle will just be in further to get the same manifold pressure. With fixed pitch, or if you're at a low enough airspeed to be out of the governing range on a C/S prop, you will have a little higher power setting.

At the end of the day, though... Don't overthink it. Fly the plane, maintain the same airspeeds as normal, and just do what you need to do to make that happen.

I dunno...seems to me if you’re at 70.71% of liftoff speed at the halfway point and wasted the first 100 feet, you’d have 100 feet to spare when you lift off.

True, but in any case you're not going to have any room to wiggle if something happens.

 

[MauleSkinner]

True, but in any case you're not going to have any room to wiggle if something happens.

Only if you assume, as most pilots seem to, that the runway is the only suitable surface in an emergency.

 

[Velocity173]

While not a high DA, 2,000 ft runway and over gross is usually a recipe for disaster. Never assume your plane will perform to book specs. Always give a buffer.

 

[luvflyin]

While not a high DA, 2,000 ft runway and over gross is usually a recipe for disaster. Never assume your plane will perform to book specs. Always give a buffer.

That's the first video I've seen of that one happening. That's a no forgiveness airport. I was with a CFI a few years ago, BFR, rental checkout, I don't remember. He pulls the power and I go into my engine out drill, in easy glide distance to W27 so I set up for it. He say's don't even think about it, find a good spot off airport. There is no where to go if you don't nail the approach. Tad bit short, you're f'd. Tad bit long, you're f'd. There was an accident there years ago just like that, engine out to W27. I'm pretty sure it was fatal. Gives credence to @MauleSkinner 's post #42 above

 

[Huckster79]

Well, you're already going to be short of power up there, so to some extent, yes. However, not much really changes. Distances in the forward direction are going to go by faster, but the plane will feel the same (same IAS) and you'll just notice your groundspeed is faster than normal.



If you're maintaining a 3-degree glidepath, and the same airspeed (which you should be), your true airspeed will be faster and thus your descent rate will also increase a little - Not a lot.



If you have a constant speed prop, no. Your throttle will just be in further to get the same manifold pressure. With fixed pitch, or if you're at a low enough airspeed to be out of the governing range on a C/S prop, you will have a little higher power setting.

At the end of the day, though... Don't overthink it. Fly the plane, maintain the same airspeeds as normal, and just do what you need to do to make that happen.



True, but in any case you're not going to have any room to wiggle if something happens.

I haven’t overthought anything... in the last 5 minutes that is

 

[flyingcheesehead]

Only if you assume, as most pilots seem to, that the runway is the only suitable surface in an emergency.

I make no such assumption... After all, I come from the Midwest, AKA the land of perfect-square-mile farm fields, many of which are great to land in.

However, we also have plenty of airports that are obstructed... Whether it's trees, a fence, power lines, or whatever, there are very few airports where I'd be OK with lifting the wheels off as the runway is ending underneath me, as performance after that is likely to suck enough that other things get in the way, like that fence and berm in the video above.

 

[Huckster79]

I make no such assumption... After all, I come from the Midwest, AKA the land of perfect-square-mile farm fields, many of which are great to land in.

However, we also have plenty of airports that are obstructed... Whether it's trees, a fence, power lines, or whatever, there are very few airports where I'd be OK with lifting the wheels off as the runway is ending underneath me, as performance after that is likely to suck enough that other things get in the way, like that fence and berm in the video above.

I was working in the hanger the other evening (scraping glue out after removing the interior) and winds we light but favored 28. A couple planes were in and out. Our hangers are on the far west end of the airport- I can barely hear run ups on 28 if at all. All the sudden I hear an engine go from idle to full bore- look out and a Cherokee 140 leaves the ground and is maybe 5-10ft off the runway as it ended. Some freaking fool did an intersection take off on a 4000 foot runway in a plane that’s not known to be a homesick angel! There’s a good way to save some Hobbs time! Shook my head and went back to lightening my old gal up.. I hope the pilot was scared enough to have learned a lesson...

 

[N1120A]

2800' is NOT a high DA. In a light, NA single, I don't consider leaning for DA until it hits 3000', and that is really only if the runway is really short. Like under 3000', or with some obstacle issues.

That said, it is good that you think about DA. I remember my first real DA experience was after I already had my PPL and was working on my instrument. Departing TUS with basically a light tail wind, at something like 48 degrees. That was certainly an experience, and it didn't help that I forgot to put the gear on the Arrow up (my CFII was there and pointed it out). Then, 39 degrees out of ABQ, which was certainly interesting, though the climb was better because we got into a headwind once making our turn into the valley. Still, 5000' for an Arrow to get up is a puckering experience.

Big Bear is a great learning experience for pilots here in Southern California, and actually a place I didn't even go till after my instrument. 6300' elevation and potential for some warm days, with terrain all quadrants except one. You have to remember that, after leaning, DA is all about utilizing ground effect in a similar way to a soft field.

 

[LongRoadBob]

This video might be a bit dated, it the lesson is still valid.

I lasted only to 19:56...could not take any more of Harry Blisse’s ignorance, the long story line and (“women!”) his wife being on the verge of discovering Harry’s “bliss”. Also waiting for the hammer to drop, finally.

Why did they feel the need to make it a story?

 

[zaitcev]

It occurred to me though, that I really had no way to quickly judge runway length vs density altitude and was wondering if anyone had a quick guide or “rule of thumb” they use in a similar situation.

I always carry the documents folder in my bag and it has a page with the DA chart (_not_ the Koch chart). It's a quick check. Unfortunately, I don't know where the authoritative source of the chart is. The FAA-H-8083-25A has a version of in the relevant section, but it's a little too small.

Do remember to think about the climb-out plan. Once in a while pilots make the required DA and takeoff distance estimates, but then cannot outclimb the terrain. I remember one guy did that at the geothermal plant airport in Dixie, Nevada, in a Bonanza. It was a Part 135 flight, too!

 

[Huckster79]

Just maintain your airspeed, and by that I mean nail your approach speed and it will work out. What will change is your ground speed, it will be faster at higher DA. That may or may not be noticeable to you. I would be more concerned in takeoff than landing, but as long as you stick to early morning operations you'll be fine.

I understand you're flying with a group, but I still recommend trying out Garden Valley to get your backcountry feet "wet"...

EDIT: Another option is Stanley (2U7). It's not confined in a canyon, but it is at 6400 MSL with a long dirt/turf runway. Smiley Creek (U87) is another option, again not in a canyon, but has a nice long grass runway and is at 7200 MSL and is an excellent eye opener to DA!

I believe we are going to both places you mention, Smiley creek is their annual ice cream stop!

 

[IK04]

When I was a full-time instructor, we went to Lake Tahoe and Flagstaff for the required high altitude checkout in the club 172.

Flagstaff is a great field for high DA operations because it is a long, skinny airport and the trees that line both sides of the runway are visible all the time during takeoffs and landings. If you recognize that you are moving faster over the ground easily, it helps reinforce the need to stick to your airspeed and use power as needed.

The climb gradient after leaving ground effect is also pretty obvious because you can use those trees as an altitude reference until you have enough altitude not to worry about it.

Flagstaff is not very busy, so there is usually not much wasted time during a practice session.

Good times...

 

[Robin Hood]

This is a great topic that we can all benefit from. I learned to fly in the hill country where DA was worth consideration. I now do most of my flying in the flat country, and I testify that it is somewhat more relaxed in the respect of DA. My advice is to use the book if your ever in doubt and add your own precautionary measures (just to be sure). Don’t be afraid to wait around for cooler air and lower DA. On the hot days that I do fly I normally load as light as is reasonable and then fly in ground affect a bit after rotation. Once my speed is 5 or 10 above my climb speed I feel more confident about pulling into a climb and not having to worry about hearing that stall horn or angle of attack. Also all of my takeoffs include flaps so that enables a shorter takeoff roll to where acceleration can be made in the air within ground affect meaning less drag on the plane.