Below Sea Level Airports

Discussion in 'Pilot Training' started by Terry, Apr 26, 2015.

  1. Terry

    Terry Line Up and Wait

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    Hi everyone, been wondering again. :rolleyes2:

    Bar Yehuda Airfield, Masada Air Field, is -1240' below sea level.

    Furnace Creek Airport, Death Valley, is -210' below sea level.

    I am heading toward these airports in a C172 at 6,000' AGL. Assuming a barometer of 29.92" and a temperature of 24*C, what would I need to do to land at either airport.

    Like I said, just wondering.

    Terry
     
  2. roncachamp

    roncachamp Final Approach

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    Descend.
     
  3. Hank S

    Hank S En-Route

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    I'm just guessing, but full flaps, idle throttle, 60 KIAS and air in the tires. Haven't flown a Skyhawk in a while.
     
  4. N801BH

    N801BH Touchdown! Greaser! Gone West

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    Where did you come up with those numbers....

    Standard day is 29.92.... 59f and 0% humidity.....:dunno::confused::confused:
     
  5. Pilawt

    Pilawt Final Approach

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    At those locations one is more likely to find 24C than ISA ...
     
  6. N801BH

    N801BH Touchdown! Greaser! Gone West

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    Yeah.... I thought about that too.....

    But he said Baro setting, not altimeter setting,.... and I figured 29.92 would be really low for that elevation...:dunno::confused:
     
  7. Cpt_Kirk

    Cpt_Kirk En-Route

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    Buy an Amphib.
     
  8. sourdough44

    sourdough44 En-Route

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    It hardly matters if the airport is 200 msl or -200 msl. It's just numbers on an altimeter, adjust accordingly.
     
  9. N801BH

    N801BH Touchdown! Greaser! Gone West

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    Nope....

    My private airport (2WY3 ) is at 8000 MSL.. The thin air makes a HUGE difference in how any plane flies...:yesnod:

    Altho 400 feet is hardly felt... :redface:
     
  10. Hank S

    Hank S En-Route

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    Yep, high DA makes quite a difference. But the question here is about LOW DA. Shouldn't be hugely different.
     
  11. N801BH

    N801BH Touchdown! Greaser! Gone West

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    Agreed....

    To be honest I thought Furnace creek was the lowest airport in the world...

    I have never heard of the other one 1200 below sea level...:redface::redface:
     
  12. Dennis McKim

    Dennis McKim Line Up and Wait

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    Per Wikipedia:
     
  13. Terry

    Terry Line Up and Wait

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    I learned at an airport that was 2,000' above sea level. (Hays, Ks.)
    At Hays, I can back the power off to 1700 rpm and will descend at 500 fpm.

    I then flew from Hays, Ks. to Wichita Falls, Texas. I backed the power off to 1700 rpm, and I stayed up in the air.

    It took me 2 attempts to get to pattern altitude so I could land.

    So, I was wondering if the airport was below sea level would this problem be worse?

    This is when I was learning to fly.

    Terry
     
  14. BillTIZ

    BillTIZ Final Approach

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    It's no different at -200ft than sea level. Use the power reductions you need, fly th IAS as you would in KS. If you are there in summer, you may find that the Density Altitude is well above sea level, or maybe even higher than your 2000 ft KS airport.
     
  15. MAKG1

    MAKG1 Touchdown! Greaser!

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    Aside from significant terrain near both locations, I would expect them to behave like any other desert airport. What are you expecting?

    Expect lots of wind, and moderately high temperatures this time of year. Just like any other low desert airport.
     
  16. Gucci Pilot

    Gucci Pilot Pattern Altitude

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    The same thing you do at airports roughly 200 feet higher :dunno:
     
  17. ahkahn

    ahkahn Line Up and Wait

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    Best thing to do is enter a downwind, then turn base, and after turning final descend until you touch pavement.

    I'll betcha a steak dinner that if your altimeter is properly set in the kollsman window you'll see the altitude drop below 0.
     
  18. N801BH

    N801BH Touchdown! Greaser! Gone West

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    :rofl::rofl::lol::lol:...

    Can I double down on that bet... I am hungry and would like a steak for dinner too..;)
     
  19. FastEddieB

    FastEddieB Touchdown! Greaser!

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    Terry,

    I think you may have misinterpreted something else that was going on.

    Consider this:

    [​IMG]

    Note that it's a straight line.

    Altitude may ever-so-slightly increase descent rate, since the TAS speed for best glide at the same IAS is higher. But the couple of knots difference over 2,000' should have been negligible, and not enough to account for what you saw.

    I'm thinking on that day you just hit some thermals that kept you up.

    Possible?
     
    Last edited: Apr 27, 2015
  20. CharlieTango

    CharlieTango Line Up and Wait

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    Last time I went to Furnace Creek it was in a group of about 20 planes and no-one had any issues.

    First time I landed at Furnace Creek was on a dark night, there is a lot of dark out there on approach. Best to fly a steep final.
     
  21. BigBadLou

    BigBadLou Final Approach

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    -1240 PA and 24C yields cca -300 DA. Nothing special. Just like flying in winter when the DA is lower due to low temperatures.

    Just fly the plane. :)
    And have fun!!
     
  22. chartbundle

    chartbundle Pattern Altitude

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    It's almost like the people who made altimeters expected it to work...

    [​IMG]
    (KTRM, 110F and -115' )
     
  23. ahkahn

    ahkahn Line Up and Wait

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    You've done 1 of 3 things here:

    1) Landed at one of the above mentioned airports.
    2) Dialed back your altimeter.
    3) Augured your plane in something fierce and lived to show the pic.
     
  24. MAKG1

    MAKG1 Touchdown! Greaser!

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    Nope, KTRM is not one of the above mentioned airports.

    There are a handful of below sea level airports in Southern California, not just one.
     
  25. warthog1984

    warthog1984 Cleared for Takeoff

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    At 1700 rpm on a cold day at sea level, you're producing a heck of a lot more power than at 1700rpm on a hot day at 3000MSL. That's the most likely cause.
     
  26. FastEddieB

    FastEddieB Touchdown! Greaser!

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    Good point.

    But do you really think that would be that noticeable?

    Most of my flying now is from airports around 2,000' AGL. Before that, most was around SL. And I have a smattering of flying out west at much higher field elevations.

    Maybe it's lack of perception on my part, but for a given rpm at a given IAS I just don't notice much difference in glide performance due to altitude.

    Curious if others do.
     
  27. bflynn

    bflynn Final Approach

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    I don't see any kind of weather equipment at L06, so I'd probably check the weather at NID and CRQ for barometer and split the difference. Then fly an 1000' AGL downwind (800 MSL), just like any other airport. Or maybe not even check the other airports, just judge it by eye.

    Was there some special question hiding in there that we're all missing?
     
  28. FastEddieB

    FastEddieB Touchdown! Greaser!

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    On second thought, with a fixed pitch prop, why would there be a large difference in power at a given rpm with altitude?

    I understand that in thinner air, a propeller is less efficient. But noticeably so over just a few thousand feet?

    Again, not that I've noticed.
     
  29. CharlieTango

    CharlieTango Line Up and Wait

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    Often my CT won't descend on final, that's why turkey vultures soar there.
     
  30. asechrest

    asechrest En-Route

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    Part of the issue might be too much reliance on specific power settings or plane configurations. Early on in training, a student needs some rigid structure to handle the fire hose effect. But I think a good instructor weans the student off of some of that rigidity and more toward a flexibility to make the plane do what you need it to do.
     
  31. Johann

    Johann Pre-takeoff checklist

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    Flying airports!
     
  32. MAKG1

    MAKG1 Touchdown! Greaser!

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    Yeah, most of my airports are at 0 AGL. Even in the mountains. :D
     
  33. FastEddieB

    FastEddieB Touchdown! Greaser!

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  34. MAKG1

    MAKG1 Touchdown! Greaser!

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    To be fair,not all airports are at 0 AGL.

    [​IMG]
     
  35. Jeff Oslick

    Jeff Oslick En-Route

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    China Lake might be vaguely useful, CRQ, not at all - hundreds of miles away and a coastal airport. There are substantial altimeter setting differences often just crossing from the LA Basin to the high desert.

    I've landed at L06 a few times. Need to be aware that winds in the valley can be very strong, and with little weather reporting, so you're pretty much on your own. If it's anything but "no clouds below 12,000" at L06, there is probably a sand storm and you need to go elsewhere...
    NWS does have weather station near Stovepipe Wells, about 15 miles from L06:
    http://forecast.weather.gov/MapClick.php?zoneid=CAZ522#.VT_XOCFVhBd

    Big Bear to Thermal is a fun flight. Nearly 7,000 drop in ~56 nm. More of a glide than a flight.
     
  36. fiveoboy01

    fiveoboy01 Pattern Altitude

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    Almost lost my soda.. ROFL
     
  37. Ghery

    Ghery Touchdown! Greaser!

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    Look carefully and you can see Bar Yehuda in this picture, taken from the fortress at Masada. And, 24C? I wish it had been that cool. 40C is closer to reality. :D
     

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  38. apr911

    apr911 Pre-takeoff checklist

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    To me, this right here is probably the best answer... Ultimately, landing at Bar Yehuda is likely to be no different than landing at any airport at sealevel... For that matter, Furnace Valley or Thermal in SoCal are likely to be the same.

    They're all airports in particularly inhospitable places (in other words deserts) where daytime temperatures are likely to soar far above the standard temps of 15C that you're density altitude will make the negative field elevation like landing at a field at sealevel.

    In fact, at 40C, Bar Yehuda would have a DA closer to the 2000ft you are used to landing at than sea level (DA at 40C would be about +1500ft).

    Ultimately, as has already been indicated, your instruments such as your altimeter will still work though reading the altimeter might be made a bit confusing due to the "unexpected" value (its not really unexpected but even expecting it, it's still easy to get tripped up when initially seeing the value) and your TAS will likely be a bit slower than your IAS (general rule of thumb is TAS is 2% higher per 1000ft in altitude gained, so going in reverse your TAS is probably 2-3% lower).

    The plane will still fly and as long as you fly the pitch to maintain your IAS at your pattern/landing speeds and use an increase/decrease in power to control your altitude/sink rate, you'll end up on the ground with no major issue.

    On the off chance you found yourself at one of these airports on a day when Density Altitude was closer to field elevation, it would be no different than flying at a near sea level airport on a cold day. Your engine will produce more power at a given setting and the wing will generate more lift so you'll need less RPM on the approach to maintain a given altitude/descent together with airspeed. All of this is likely to contribute to a long(er) landing since the plane is likely to want to float above the runway, especially when coupled with ground effect, and one thing you definitely dont want to do is force the airplane to the ground before its done flying.


    And on the really really off chance you found yourself at one of these airports on a day with negative density altitude (in addition to the already negative pressure altitude), it'd be similar to flying in places with extreme temperature conditions (Antarctica, Arctic Circle, Alaska, Montana, etc) though probably without the concern for icing of the wings, fuel (yes AvGas will freeze) or carburetor... You will need to be careful not to overpower the engine. The FAA specifically provides the following takeoff warning for winter flying/low density altitude airports:


    • Do not overboost supercharged engines. This is easy to do because at very low density altitude, the engine "thinks" it is operating as much as 8,000 feet below sea level in certain situations. Care should be exercised in operating normally aspirated engines. Power output increases at about 1% for each ten degrees of temperature below that of standard air. At -40 degree temperatures (-40 is the same in F and C), an engine will develop 10 percent more than rated power even though RPM and MP limits are not exceeded.
     
    Last edited: May 6, 2015
  39. MAKG1

    MAKG1 Touchdown! Greaser!

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    It's not always 40 C at the Dead Sea.

    I've been there on a "nice" day. In January. It was closer to 20 C.

    And there is occasionally snow in the nearby mountains. Jerusalem is funny when it snows. The locals act like Texans and shut down the country.
     
  40. apr911

    apr911 Pre-takeoff checklist

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    Fair enough, but even a 20C day would give you a DA that is 200-300 feet higher than field elevation and according to this list:

    http://en.wikipedia.org/wiki/List_of_places_on_land_with_elevations_below_sea_level

    With the exception of Tiberias, Dead Sea and Sea of Galilee, there is no other place consisting of dry land with an elevation more than 510 ft below sealevel and the vast majority of the locations are more in the -50 to -200 ft range (I suppose to hear climatologists tell it, this will soon change)