First Encounter With Density Altitude

itsjames2011

itsjames2011

Pre-takeoff checklist
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Chicopee MA
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James
Hey everyone,

I earned my PPL in Oct 2013 and have about 80 hours total time. I'm spoiled and am always into and out of airports at sea level but today's trip was not usual. Below is a summary of the situation and any advice would be appreciated. I know this is probably not out of the ordinary for some of the folks here but I still have LOTS of learning to do. :)

Today I departing Pittsfield KPSF in my Warrior II PA-28-161. Field elevation is 1188 and temp was 26c which gave me a density altitude of about 2555ft. I have never dealt with an elevated airport let alone in hot weather so I pulled out the POH, did all of my calculations, and determined I had enough runway not only to take off but also to abort at rotation should something go wrong. That 5700 foot runway was a godsend. I held off on my rotation to 60 kts, accelerated in ground effect to 79 kts, and then brought up the nose to hold 79kts and sure enough I had a 400ish ft per min climb as the manual predicted.

Anything else a new pilot can learn from this? Did I miss anything important?

James
 
Excellent learning experience. Remember to always rely on the airspeed indicator (assuming it's working properly) for both take off and landing, use the same speeds and don't worry about what appears to be faster speeds out the window.

Also remember the altitude chart for DA in the POH doesn't go past 7000 MSL - Piper factory is at sea level and they never considered planning for higher altitudes.

[you really don't want to know what the DA was in Denver today]
 
Just to make sure I fully understand what you're telling me, as long is the airspeed indicator is working I can rotate and climb at the same indicated airspeed as normal as long as I keep in mind the decreased rate of climb and longer take off roll?
 
...good job.

For me, I fly a high performance plane (235HP) out of a field with ~800' elevation. I live in Texas so it's hot and the DA can get into the low 3000' range. I find I don't really do anything different. I don't even start leaning until around 3-4k feet anyway so if I'm at a field where I don't need to make any adjustments like that (ie; mixture rich works) then I'm not pulling out any paperwork since I know from experience that I can get my plane at near gross up off the runway in less than 1500'.

Now, I've already contemplated trips to El Paso, TX in the summer (it's 4000' feet there so DA will come into play for sure) and various places in eastern NM where DA is in play as well. I'll definitely be doing my homework there.
 
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itsjames2011 said:
Just to make sure I fully understand what you're telling me, as long is the airspeed indicator is working I can rotate and climb at the same indicated airspeed as normal as long as I keep in mind the decreased rate of climb and longer take off roll?
Click to expand...

Yes but the pitch attitude will be different for that airspeed.
 
NJP_MAN said:
Yes but the pitch attitude will be different for that airspeed.
Click to expand...
Since we are working on a decreased performance situation, I would think that we would have a higher angle of attack and slower rate of climb at 79kts with a DA of 2500 than we would with a DA of 500.

When my CFI told me I had to spend $55 on a POH last year I was not thrilled but when I realized I was at a higher altitude airport with a hot temperature I was quite relieved that it was in my bag. :)
 
Not to rain on your parade, but 2500 DA is nothing. You did almost all the right stuff for higher DA, and identifying abort points is important. If the DA were above 5000, you would have needed to lean for takeoff.

The big takeoff risks at high DA are excessive pitch trying to get sea level climb performance, wrong Vy (it is indicated SLOWER at high altitude), overloading, taking off full rich, and failure to identify a short field. Winds and rising terrain are dominant risks at altitude.

The highest DA I've taken off in in a Warrior is 8500. Highest DA overall in a Warrior is nearly 12000 (using ridge lift to get over a 10500 ridge).

A Warrior (or even an Archer or Arrow) isn't the best platform for real high DA. Even a 172 can do better. Cessna retracts can do a lot better.

You would benefit substantially from some mountain training. It's quite a lot of fun.
 
MAKG1 said:
Not to rain on your parade, but 2500 DA is nothing. You did almost all the right stuff for higher DA, and identifying abort points is important. If the DA were above 5000, you would have needed to lean for takeoff.

The big takeoff risks at high DA are excessive pitch trying to get sea level climb performance, wrong Vy (it is indicated SLOWER at high altitude), overloading, taking off full rich, and failure to identify a short field. Winds and rising terrain are dominant risks at altitude.

The highest DA I've taken off in in a Warrior is 8500. Highest DA overall in a Warrior is nearly 12000 (using ridge lift to get over a 10500 ridge).

A Warrior (or even an Archer or Arrow) isn't the best platform for real high DA. Even a 172 can do better. Cessna retracts can do a lot better.

You would benefit substantially from some mountain training. It's quite a lot of fun.
Click to expand...
I have no doubt that my planning was probably overkill. As a low time pilot with my fiancee and 10 year old in the airplane, I feel like when I run into a situation I have not yet experienced, I need know all of the variables.

That's really the beauty of this form. It gives me the opportunity to draw on the experience of others. :cool:
 
MAKG1 said:
Not to rain on your parade, but 2500 DA is nothing. You did almost all the right stuff for higher DA, and identifying abort points is important. If the DA were above 5000, you would have needed to lean for takeoff.

The big takeoff risks at high DA are excessive pitch trying to get sea level climb performance, wrong Vy (it is indicated SLOWER at high altitude), overloading, taking off full rich, and failure to identify a short field. Winds and rising terrain are dominant risks at altitude.

The highest DA I've taken off in in a Warrior is 8500. Highest DA overall in a Warrior is nearly 12000 (using ridge lift to get over a 10500 ridge).
Click to expand...
nyah nyah nyah....come to Colorado. DA in the afternoon is over 9500 at pretty much every airport around Denver (12 at last count not including DIA).
A Warrior (or even an Archer or Arrow) isn't the best platform for real high DA. Even a 172 can do better. Cessna retracts can do a lot better.

You would benefit substantially from some mountain training. It's quite a lot of fun.
Click to expand...
 
Good job.

I took some of the guesswork out of it and installed an AOA indicator. :redface:
 
itsjames2011 said:
Hey everyone,

I earned my PPL in Oct 2013 and have about 80 hours total time. I'm spoiled and am always into and out of airports at sea level but today's trip was not usual. Below is a summary of the situation and any advice would be appreciated. I know this is probably not out of the ordinary for some of the folks here but I still have LOTS of learning to do. :)

Today I departing Pittsfield KPSF in my Warrior II PA-28-161. Field elevation is 1188 and temp was 26c which gave me a density altitude of about 2555ft. I have never dealt with an elevated airport let alone in hot weather so I pulled out the POH, did all of my calculations, and determined I had enough runway not only to take off but also to abort at rotation should something go wrong. That 5700 foot runway was a godsend. I held off on my rotation to 60 kts, accelerated in ground effect to 79 kts, and then brought up the nose to hold 79kts and sure enough I had a 400ish ft per min climb as the manual predicted.

Anything else a new pilot can learn from this? Did I miss anything important?

James
Click to expand...

:rofl: No, you didn't miss anything, you did fine. The performance loss is a sloping one, it would be good if on vacation somewhere in high altitudes you try 7000' as well.
 
itsjames2011 said:
I have no doubt that my planning was probably overkill. As a low time pilot with my fiancee and 10 year old in the airplane, I feel like when I run into a situation I have not yet experienced, I need know all of the variables.

That's really the beauty of this form. It gives me the opportunity to draw on the experience of others. :cool:
Click to expand...

It would really be better to consult with a CFI, mentor pilot or all of us BEFORE you try something new. I understand that is not always possible. Since my PP, I have always been hauling my wife and two children. I too always do alot of planning before the flight. You are doing good.

Watch out for that first landing on a hilltop runway with a 15 kt headwind. Remember it flows like water and visualize that. I found out that a 160 hp 172 may not be able to outclimb the downward flow of air on 1/2 mi final. I ask my CFI after I returned. Since then, I fly a high approach angle and plan on landing a little farther past the numbers(if long enough rwy). 260 HP and CS made a world of difference too.
 
MAKG1 said:
Not to rain on your parade, but 2500 DA is nothing. You did almost all the right stuff for higher DA, and identifying abort points is important. If the DA were above 5000, you would have needed to lean for takeoff.

The big takeoff risks at high DA are excessive pitch trying to get sea level climb performance, wrong Vy (it is indicated SLOWER at high altitude), overloading, taking off full rich, and failure to identify a short field. Winds and rising terrain are dominant risks at altitude.

The highest DA I've taken off in in a Warrior is 8500. Highest DA overall in a Warrior is nearly 12000 (using ridge lift to get over a 10500 ridge).

A Warrior (or even an Archer or Arrow) isn't the best platform for real high DA. Even a 172 can do better. Cessna retracts can do a lot better.

You would benefit substantially from some mountain training. It's quite a lot of fun.
Click to expand...



Last winter it was so cold the DA here was -1500'. Yes, minus 1500 feet. :lol:
 
itsjames2011 said:
Just to make sure I fully understand what you're telling me, as long is the airspeed indicator is working I can rotate and climb at the same indicated airspeed as normal as long as I keep in mind the decreased rate of climb and longer take off roll?
Click to expand...

Yes. Airspeed is everything. :D

I like the fact you are thinking about DA. Don't let it spook you, just be aware of it. Lots of planes fly into mountain airports all the time. Laramie, WY is 7,300'. Piece of cake as long as you know to lean for landing and take off. ;)
 
Yep, there are times that the fact I learned to fly at BJC has really come in handy.
I also never confused AGL with MSL as a result.
 
Geico266 said:
Yes. Airspeed is everything. :D

I like the fact you are thinking about DA. Don't let it spook you, just be aware of it. Lots of planes fly into mountain airports all the time. Laramie, WY is 7,300'. Piece of cake as long as you know to lean for landing and take off. ;)
Click to expand...

Well, airspeed is indeed everything, but you don't climb at the same speed. There ain't no cruise-climb at high altitude unless you find rising air. And Vy is slower and Vx is a little faster. You do approach at the same speed, but the pattern needs to be a bit bigger to accommodate the higher ground speed.
 
Geico266 said:
Last winter it was so cold the DA here was -1500'. Yes, minus 1500 feet. :lol:
Click to expand...
I do miss the performance of winter. I am up in Massachusetts and for a good portion of my initial hour building, DA of -2500 was the norm :D
 
MAKG1 said:
Not to rain on your parade, but 2500 DA is nothing. You did almost all the right stuff for higher DA, and identifying abort points is important. If the DA were above 5000, you would have needed to lean for takeoff.

The big takeoff risks at high DA are excessive pitch trying to get sea level climb performance, wrong Vy (it is indicated SLOWER at high altitude), overloading, taking off full rich, and failure to identify a short field. Winds and rising terrain are dominant risks at altitude.

The highest DA I've taken off in in a Warrior is 8500. Highest DA overall in a Warrior is nearly 12000 (using ridge lift to get over a 10500 ridge).

A Warrior (or even an Archer or Arrow) isn't the best platform for real high DA. Even a 172 can do better. Cessna retracts can do a lot better.

You would benefit substantially from some mountain training. It's quite a lot of fun.
Click to expand...

I've left TVL on 9,000'+ DA's three times:

1. Beech Debonair, loaded with me and a CFI. Departed 18 straight out, cleared the pass easily. I was doing a mountain checkout.

2. Turbo Arrow. Actually that was near 10,000' DA that day. It was freakin' hot. Departed 18, needed to do a circle to clear the pass. The TA has a mediocre climb rate to begin with, but it can maintain almost the same mediocre climb rate at 10,000 feet. I've taken it as high as 17,500 just for ****s and giggles.

3. Arrow II. Flew in that day with four people. Dumped two pax off and then I flew the plane back from the right seat with the Other Guy in the left seat. Departed 36, gained elevation over the lake in a slow circling climb before heading over the ridge. Same way I would do in a 172 on a hot day.
 
It sounds like you did everything correctly. Just remember to lean if the DA is over 3000 ft. I fly a lot in northwest New Mexico and have seen the density altitude over 10,000, like a couple days ago. I have watched some small planes land and not be able to take off until very early the next morning. On the other side I used to fly out of Barrow, AK, and in winter I have seen DA as low as -5000 feet. Really good climbout with that.
 
I've left TVL in a 180 HP 172N with 9000+ DA, loaded to 2300 lb (~90% of max gross). If you're ready for the 300 FPM climb rate and you take off on 36 (toward the lake; that's the direction with no rising terrain) with no configuration errors, it can do it. It's a really long runway, which makes it rather comfy. You can be out of ground effect while still only halfway down, even on a stupid-hot day.

Turbocharging changes everything at DA like that. My comments only work for NA aircraft.

I'm not sure I would like to arrive at TVL loaded to max in an NA Arrow. A go-around would be a bit too "interesting," though landing performance is far better than ample.
 
flyingron said:
Yep, there are times that the fact I learned to fly at BJC has really come in handy.
I also never confused AGL with MSL as a result.
Click to expand...

Very true. Lots of folks who don't usually fly around big hills freak out when I mention I fly from Denver to Salida or Leadville at 12.5K. What they don't understand is the 12.5K is MSL, but I'm flying at 2000 AGL.

On the other hand, at Leadville, the DA can easily be 12-13K or more.
 
Zeldman said:
It sounds like you did everything correctly. Just remember to lean if the DA is over 3000 ft.
Click to expand...

The specific number seems to vary with aircraft.

Cessna single POH's seem to say 3000. PA28s say 5000. Make sure you're familiar with the high altitude procedures for the aircraft you're flying. 177s, for instance, have a fuel pressure gauge (labeled as fuel flow) you're supposed to use to lean for takeoff, and it's different from the leaning procedure at altitude.
 
With truly high density altitude, also keep in mind that when landing, your groundspeed will also be much higher when coming down final and the visual experience that produces has caused a lot of low-experienced pilots to slow down too much and stall on final. I was prepared for this effect and have witnessed it firsthand during my two trips to Idaho in my RV-6 these past couple years. Just by judging your groundspeed on final, you'd swear you must be landing with a 15-20kt tailwind, but you're not.

Even though I've always been a flatlander pilot, I learned pretty quickly what to do and not do when flying in and out of high density altitude mountain airports. The effect on takeoff performance can be frighteningly dramatic. For instance, here at my home airport, elevation 1000' MSL my little RV is off the ground and climbing at 1200 FPM after a 300' takeoff ground roll. But at Stanley Idaho, elevation 6400MSL, on a warm day the density altitude was well over 9000'. The runway there is 4300 feet long but only the north 1600' is paved, the rest is gravel. I had hoped to be off the ground before the end of the paved portion and even leaned for peak RPM and putting in 10 degrees of flaps, it took almost every bit of that 1600' to get airborne and after getting the airspeed up to normal cruise-climb speeds I finally established a climb of only a few hundred FPM. It felt just like I was back in my old Cherokee 140 on a hot Texas summer day instead of a hotrod RV-6.
 
When I took off from Lee Vining (el. 6800) on a hot day in a 177RG, that 4000 feet of pavement was a marginally short field. At sea level DA, I can get it off in less than 1000.
 
murphey said:
On the other hand, at Leadville, the DA can easily be 12-13K or more.
Click to expand...

One of the pilots at my local airport who's been to Leadville many times always says as long as you're taking off to the south from Leadville, all you need to do is be able to get 50' off the ground and hold that altitude and from there you can get all the way back to Texas without climbing any higher. :lol:

BTW, there's an old rule of thumb that says unless you can achieve 75% of your takeoff airspeed by the time you've used up 50% of the runway length, you're not gonna make it.

ETA: http://www.youtube.com/watch?v=5coMjTwQYpk
 
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murphey said:
Very true. Lots of folks who don't usually fly around big hills freak out when I mention I fly from Denver to Salida or Leadville at 12.5K. What they don't understand is the 12.5K is MSL, but I'm flying at 2000 AGL.

On the other hand, at Leadville, the DA can easily be 12-13K or more.
Click to expand...

Of course, I had a different problem getting checked out when I moved down to sea level. About five minutes into the flight the instructor asked if I was ever going to throttle back. Now there's an interesting concept, says i. We never moved the throttle off the firewall in Denver until we were abeam the numbers on landing.
 
There are two elements of DA, pressure altitude and heat. If in doubt, first look at the POH and the tables the manufacturer provides for takeoff roll, climb and landing.

If in the mountains you also gotta be aware of turbulence, especially mountain wave. Lenticular clouds are especially important in mountain valleys, that is a big tip on the wave being present.

If DA is 40-50% over field altitude you can double your roll and lose half your climb power. Also remember that every aircraft has a DA ceiling. If DA at pattern altitude is anywhere near your DA ceiling, then you should not fly that day.
 
FastEddieB said:
Well, maybe in theory, but I have never seen a ceiling published in terms of DA.
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Actually you probably have, it just wasn't stated exactly that way. Typically the service ceiling listed in a POH or AFM is for "standard conditions" which means the altitude is equal to the DA.
 
FastEddieB said:
Well, maybe in theory, but I have never seen a ceiling published in terms of DA.
Click to expand...

They all are.

A Cessna 172N may have a published ceiling of 14100, but you'll have a real hard time getting it over 12000 in summer without resorting to glider tactics.
 
Good job thinking about all of the potential complications DA may present. You can never be too careful. I am based out of an airport near Colorado Springs. Our field elevation is 6800 ft ish. Tomorrow my wife and I leave for Oshkosh via the Airventure Cup race. It is always fun to step down in altitude on the way over. I guess I sort of experience the opposite of what you do. My plane feels like a rocket ship at sea level. I fly a Gobosh just like the blue one there at Northampton.

Carl
 
NJP_MAN said:
I'm pretty sure on a day with 110F temps when I pitch for Vy it looks a lot different than if I do the same at sea level on a cool day.
Click to expand...

At first, I thought that at high DA's you must push the pitot through the air faster to get the same IAS, so I would expect the aerodynamics to be the same once you got to that speed, so the pitch for climb would be the same.

On further reflection, yes - Vy decreases with altitude. Hence the pitch for the desired climb speed would be steeper.

But it still seems that for any given IAS climb speed, the pitch would be the same.

Right?
 
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The difference in Vy over a few thousand feet DA is a couple of knots at most, so I find it hard to believe the pitch change is perceptible.
 
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