Density Altitude

[Mooney217RN]

There was a recent thread on DA that I was browsing here on Mooney Space, and I felt compelled to start a new one.  We're quickly moving into the season where density altitude will become an issue to contend with.  Please note that I am not a CFI, but a pilot based at a high altitude airfield in mountainous terrain who has flown thousands of hours in my Mooney in these conditions.

Density Altitude is the silent, invisible killer.  I have seen many an accident caused by DA.  The #1 way to ensure that you're not one of those statistics is avoidance.  The #2 way is to get a mountain checkride BEFORE you head into the mountains on your own.  Don Kaye out here on the west coast can do that for you.

I am based at TRK.  Every single airport in this region has it's unique attributes, but Truckee is by and large the most challenging.  We deal with updrafts, downdrafts, wind shear, high winds, crosswinds, terrain, thermals and all of that mixed in with density altitude.  I took off this morning to practice some landings.  At 0830 the DA was in excess of 7,000'

Other airports in this region are easier to deal with, but each has its challenges.  The Nevada side of the state line is notorious for turbulence.  Lake Tahoe Airport is probably the easiest to operate out of, and it has the most runway outside of Reno.  But the terrain spooks a lot of people there.

Here are some pointers for those who venture into the mountains and have to deal with density altitude.  Fly early morning when it's coolest; don't load up on fuel; don't go out at maximum gross weight; fly your airspeeds, plus a few knots for safety's sake; expect to land long; expect to use more runway on departure; fly over the terrain as high as possible; you're speed over ground will be faster than you are accustomed to on the runway and in the pattern - fly your airspeeds, don't be fooled by visual clues; watch your temps - with less "air" you're oil & CHT temps will rise quicker and won't fall so easily; lean your mixture for best performance (normally aspirated engines); don't make shallow or steep approaches, stablized approaches on or slight above speed are best; don't try a short field landing in a density altitude environment.  One of the things I noticed years ago is that your airspeed will bleed off quicker than normal and your stall will occur faster than usual - you have less lift and less air density, so this makes perfect sense.  Do NOT fly behind the power curve under any circumstances; we had a couple of airline pilots we lost a few years back who did that, we couldn't find them, but eventually spotted the plane short of the runway about 1500' from the threshold in the scrub.  The suspicion is that they were low, slow and behind the power curve, just flew it into the ground as the aircraft caught the downside of a thermal on short final.

Mountain flying is very rewarding, and it can be a new challenge for many to overcome.  When you head up into the mountains, we want you to visit again and visit often.  The best way to do that in your Mooney is to have a mountain checkride before you load up the bird and fly up the hill.

[RobertGary1]

The there is me who loads up to gross and crosses over the Sierras at 16,000 feet in the summer afternoons. 

[carusoam]

Great insight 217RN!

Thanks for sharing all of the details...

Best regards,

-a-

[RJBrown]

I learned how to fly in Denver at 6880’msl in the summer. The DA was announced on the atis. I never gave DA a second thought. Learning in those conditions Everything seemed normal. It was that first flight to Palomar California that felt strange as can be. That 182 seemed to never want to quit flying. Going from Denver to the California coast was a learning experience but going the other way, sea level to high altitudes could be dangerous without training.
I was the last person to survive a flight in Mooney N3768N an F model when I flew from Spokane to Denver back in 1996.

Early the next morning 2 freshly minted, Florida trained, CFIs took it into the mountains without proper training and failed to return.

https://planecrashmap.com/plane/co/N3768N/

After owning a Rocket I bought a 1990 MSE, the J behind me in my avatar picture. It’s inability to get to and sustain altitude is why I sold it. I’ve lost friends who couldn’t outclimb the trees near Aspen.     https://www.accidents.app/summaries/accident/20001212X21427
 Just never felt safe in the J like I did in the K/Rocket. 
Get training, fly early, be careful. It’s a different world up high.

He was flying and his wife took this picture of me just a month before. Breaks my heart to think about them still today. 
Fly smart, Be safe out there. Somebody out there loves you.

Edited May 17, 2021 by RJBrown

[Yetti]

looks like parts of the plane are still there.

There is another image of a plane in more southern colorado where they almost made it over the ridge.  

 

[Yetti]

This one

https://planecrashmap.com/plane/co/N58119/

[Tim Jodice]

It sounds like a turbo is almost a must.

[midlifeflyer]

I've been lucky. Learned to fly in New England. Then 20 years in Denver. Now in the southeast. It all seems normal to me,

[FlyingDude]

12 minutes ago, Tim Jodice said:

It sounds like a turbo is almost a must. 

Turbo can give false sense of safety. Of course, your engine will not suffer as much but your prop and wings will have reduced performance due to higher density altitude. So it's not a "get out of trouble for free" card...

(CFI and plenty mountain flying experience in SW Alps)

[FlyingDude]

On 5/14/2021 at 6:11 PM, Mooney217RN said:

your airspeeds, plus a few knots for safety's sake

I concur with your advice points.

Just my 2c worth: Vx and Vy are not constant across all altitudes and weights. At the service ceiling, only 1 speed (somewhere between Vx and Vy, around best glide) keeps you afloat, 1 kn slower or 1kn faster, and you sink. POH has valuable info, and one can also experiment over flat states: take off from your home base with minimum safe fuel and at MTOW and once you reach 7000' do a stall. You won't recover in 150' per PPL PTS as you did at 3000'. Do slow flight, try climbing at Vx and Vy and learn your new speeds for those altitudes. It won't substitute for a mountain check out, but it'll be a good teaser

 

 

[Hank]

37 minutes ago, FlyingDude said:

I concur with your advice points.

Just my 2c worth: Vx and Vy are not constant across all altitudes and weights. At the service ceiling, only 1 speed (somewhere between Vx and Vy, around best glide) keeps you afloat, 1 kn slower or 1kn faster, and you sink. POH has valuable info, and one can also experiment over flat states: take off from your home base with minimum safe fuel and at MTOW and once you reach 7000' do a stall. You won't recover in 150' per PPL PTS as you did at 3000'. Do slow flight, try climbing at Vx and Vy and learn your new speeds for those altitudes. It won't substitute for a mountain check out, but it'll be a good teaser

 

 

With my Mooney, the CFII simulated high DA by taking off with 23" / 2700, but there's no good way to simulate a High DA landing.

[FlyingDude]

4 minutes ago, Hank said:

With my Mooney, the CFII simulated high DA by taking off with 23" / 2700, but there's no good way to simulate a High DA landing.

How about landing with ~12" MAP? The tad power will give you some float similar to what happens at 8000' DA airports.

[Hank]

Just now, FlyingDude said:

How about landing with ~12" MAP? The tad power will give you some float similar to what happens at 8000' DA airports.

But that won’t show the different handling and loss of lift. We all practice 90 knots to 200 agl, take off the foggles and land, this isn't much different. 

[FlyingDude]

Just now, Hank said:

that won’t show the different handling and loss of lift

That's correct, but neither would 23"/2700 rpm at take off. It only stimulates the loss of power. 

Anyway. High altitude stalls and slow flight have been an eye opener my students... So I wanted to share that with the group...

[dogbocks]

3 hours ago, Tim Jodice said:

It sounds like a turbo is almost a must.

I have departed truckee on a hot afternoon with 9k DA in my O2 at max gross. No turbo, it was fine.

before anyone freaks out I checked the book and seemed like I beat the take off roll. Just have to keep the climb mellower than usual since the motor gets pretty hot.

[carusoam]

Dogb,

Does your O2 still have the 280hp it was born with?

Speaking of CHT control... what is the max FF you see during T/O?

Best regards,

-a-

[dogbocks]

1 hour ago, carusoam said:

Dogb,

Does your O2 still have the 280hp it was born with?

Speaking of CHT control... what is the max FF you see during T/O?

Best regards,

-a-

Yep still 280 but with the 3 blade top prop already. planning on 310 at some point, just need to dig around in the couch cushions for 7 AMU

 

FF- of the top of my head 23-something. It has was checked/calibrated last summer when trying to track down a hot CHT issue, so it is spot on according to the spec.

 

Departing Mammoth, Truckee and Bridgeport (3800 foot runway at 6.5k feet) on hot days always get off the ground with lots of runway left, and *could* climb at 1000fpm, I would just melt the engine so I have to keep it to 400ish fpm at least until in cooler air. Not sure if that is a limitation for other Mooneys M20R or otherwise. Would be interesting to know. 

[carusoam]

db,

There are a few discussions around here for FF and the IO550...

Mostly stemming from the 310hp version...  where 27.2gph (?) isn’t quite enough to comfortably cool the CHTs...

The Missile with 300hp has the same challenge....

Expect the O<3s may benefit from additional FF...

The maintenance books probably give a range... to select from...   

Often, the middle of the range gets targeted...

You may want to specifically choose the max limit of the documented range...

PP thoughts only not a mechanic...

Best regards,

-a-

[RobertGary1]

13 hours ago, Tim Jodice said:

It sounds like a turbo is almost a must.

I don’t think so. I’ve been flying my F in the southwest for 20 years. Just need to understand it’s a different plane when it’s hot. 

[RobertGary1]

9 hours ago, dogbocks said:

I have departed truckee on a hot afternoon with 9k DA in my O2 at max gross. No turbo, it was fine.

before anyone freaks out I checked the book and seemed like I beat the take off roll. Just have to keep the climb mellower than usual since the motor gets pretty hot.

I’ve done it in my F as well. Just don’t pull back to your usually pitch attitude on take off. Give it some time but it flys. 

[Mooney217RN]

20 hours ago, RJBrown said:

I learned how to fly in Denver at 6880’msl in the summer. The DA was announced on the atis. I never gave DA a second thought. Learning in those conditions Everything seemed normal.

Exactly, to you and me, we don't know any different.  it's when people travel to locales where DA is a daily issue that accidents sadly happen.  I tell everyone, things just happen faster with density altitude.  right now, DA is 7,100' and the temperature is 15C/59F.  Winds are forecast to be 240 @ 14 G28.  Now mix in terrain, winds that are 40-50 degrees off the runway heading, updrafts, downdrafts, wind shear, thermals and turbulence.  it's a wrestling match for certain.  And it's only 0930 here.  Once the temps rise more, DA will be up over 8,000'

Edited May 18, 2021 by Mooney217RN

[RobertGary1]

26 minutes ago, Mooney217RN said:

Exactly, to you and me, we don't know any different.  it's when people travel to locales where DA is a daily issue that accidents sadly happen.  I tell everyone, things just happen faster with density altitude.  right now, DA is 7,100' and the temperature is 15C/59F.  Winds are forecast to be 240 @ 14 G28.  Now mix in terrain, winds that are 40-50 degrees off the runway heading, updrafts, downdrafts, wind shear, thermals and turbulence.  it's a wrestling match for certain.  And it's only 0930 here.  Once the temps rise more, DA will be up over 8,000'

I think being a glider pilot helps too. There are times over the Sierras in my Mooney where I'll get a good updraft and I'll circle in it a bit because I know there is a leeward side coming up. I'm not a fan of the traditional mountain flying techniques of 45 degrees, canyon turns, etc. No reason to cross the Sierras with less than 2,000-3,000 between you and any terrain within 5 miles. Now, if you're doing it in a Cessna 150 its another story. But in a Mooney just go high. Every Mooney model can go high.

 

-Robert

[1964-M20E]

I'm manly a flat lander but I did spend some time in Idaho Falls flying in that region during the summer and fall time frames.  Certainly a different feel taking off in the afternoon sometimes I would check to make sure the engine was still running.  Most of my flights were full fuel and solo.  Density altitude does make a difference.

[midlifeflyer]

18 hours ago, Hank said:

With my Mooney, the CFII simulated high DA by taking off with 23" / 2700, but there's no good way to simulate a High DA landing.

It's only a partial simulation. It doesn't simulate the loss of lift and prop efficiency. But it's better than nothing.

[RobertGary1]

2 minutes ago, midlifeflyer said:

It's only a partial simulation. It doesn't simulate the loss of lift and prop efficiency. But it's better than nothing.

I agree with that. I've never felt that simulation technique was very helpful. Felt it was more how a flatlander thought it would be.

-Robert