ATC assigned altitude?

It used to be that when we were assigned an en route altitude we held
it, plus or minus a needle width or so -- husbands trained as
engineers are apt to be a little compulsive about things like that.
Well, we had a long discussion with another pilot who had different
advice. He suggested, since we are in a low winged airplane, we hold
assigned less 50 feet or so -- if a high winged airplane, he'd have
recommended assigned plus 50. His obvious intent is to avoid en route
conflicts. It seems like a cheap insurance policy to me, but how real
is the threat? Does anyone have an idea on how often there are
altitude conflicts when on an IFR flight plan?

We have agreed on VFR cross country flights (something that we very
rarely do) we will hold that kind of offset to the altitude rule as a
matter of routine: you might consider doing that too.

"Tina" wrote in message
...
snip
We have agreed on VFR cross country flights (something that we very
rarely do) we will hold that kind of offset to the altitude rule as a
matter of routine: you might consider doing that too.

Why? I'm sorry but I've never heard of this practice and it seems to me that
if everyone did it, what would be the difference of doing what you're
suggesting as opposed to sticking with the X-thousand + 500 feet (VFR)????

I'm not trying to be argumentative - just wondering...

Harry
PP-ASEL
VFR only

In article ,
Tina wrote:

We have agreed on VFR cross country flights (something that we very
rarely do) we will hold that kind of offset to the altitude rule as a
matter of routine: you might consider doing that too.

That's a great way to use up a significant chunk of the error budget.
(error budgets being something engineers should understand).

--
Bob Noel
(goodness, please trim replies!!!)

Bob, we fully appreciate error budgets and propagation of errors
analysis. Never the less if most VFR traffic is 'trying' to fly at
the correct hemispheric altitude (especially those who tend to fly as
high as reasonable) , and we bias our choice of altitude to be under
the mean altitude of the others, we will probably have reduced an
already small risk to one even smaIller.

I don't don't know the statistics for altitude holding accuracy in the
less than 12000 feet VFR XC world, but would not be surprised if the
S. D. is the order of 50 or 80 feet.

I also don't know the stats on near misses (or worse) during the
cruise phase of VFR XC but am trying to find out. Near misses are
going to be very much under reported, aren't they?

I've offered an argument for not staying at the exact altitude during
VFR XC , and am interested in learning some reasonable rebuttals. I
did offer one for not maintaining the exact expected altitude and hope
someone can offer compelling reasonings as to why those reasons are
not valid.

On Sun, 18 May 2008 14:30:55 -0400, Bob Noel
wrote in
:

That's a great way to use up a significant chunk of the error budget.

That was my first thought too.

However, it also brought to mind a somewhat tense situation I
experienced while VFR transiting over KLAX via the Special Flight
Rules Area: http://skyvector.com/#35-24-3-2785-2374

The ledged for the LAXSFRA is on the VFR Terminal chart (accessible by
clicking the Charts icon at the top of the page at that link above),
and basically indicates that SE bound flights cross over the KLAX
runways at 3,500' and NW bound flights at 4,500' squawking 1201 and
communicating air-to-air on 128.55 MHz with periodic self announced
position reports. ATC is not involved.

I was flying a low-wing, and announced my position as over the
southern boundary of the field, and immediately subsequent a Cessna
reported being at the same position and altitude. I wanted to take
evasive action, but without the Cessna in sight, there was no good way
of knowing exactly what that might be. I announced again, and so did
the Cessna, but we did not sight each other. The atmosphere got more
tense as the moments ticked by, and I kept expecting the sounds of
impact at any second. I considered maneuvering again, but finally
decided, that currently I was okay, and doing nothing would likely not
change that.

I suppose I could have assumed that the Cessna was below me, and
climbed a 100', but I didn't.

"Larry Dighera" wrote in message
...
On Sun, 18 May 2008 14:30:55 -0400, Bob Noel
wrote in
:
...
I was flying a low-wing, and announced my position as over the
southern boundary of the field, and immediately subsequent a Cessna
reported being at the same position and altitude. I wanted to take
evasive action, but without the Cessna in sight, there was no good way
of knowing exactly what that might be. I announced again, and so did
the Cessna, but we did not sight each other. The atmosphere got more
tense as the moments ticked by, and I kept expecting the sounds of
impact at any second. I considered maneuvering again, but finally
decided, that currently I was okay, and doing nothing would likely not
change that.

http://wingsandwheels.com/page4.htm

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

On Sun, 18 May 2008 20:33:45 -0400, "Capt. Geoffrey Thorpe" The Sea
Hawk At Wow Way D0t C0m wrote in
:

"Larry Dighera" wrote in message
.. .
On Sun, 18 May 2008 14:30:55 -0400, Bob Noel
wrote in
:
...
I was flying a low-wing, and announced my position as over the
southern boundary of the field, and immediately subsequent a Cessna
reported being at the same position and altitude. I wanted to take
evasive action, but without the Cessna in sight, there was no good way
of knowing exactly what that might be. I announced again, and so did
the Cessna, but we did not sight each other. The atmosphere got more
tense as the moments ticked by, and I kept expecting the sounds of
impact at any second. I considered maneuvering again, but finally
decided, that currently I was okay, and doing nothing would likely not
change that.

http://wingsandwheels.com/page4.htm

That's an interesting device. I'm not sure it would have been too
useful in the case cited above. The vertical resolution isn't going
to be better than the +/- 100' of Mode C, and it's not clear that it
can resolve the lateral position of aircraft in close proximity; it
appears to just go into alarm when one gets closer that the preset
distance selected. It may have been useful when our two aircraft were
more distant and converging however. Thanks for the information.

Larry Dighera writes:

I considered maneuvering again, but finally
decided, that currently I was okay, and doing nothing would likely not
change that.

You did the logical thing. If you and the other aircraft had indeed been in
exactly the same position, you would have already collided. Obviously you
were not in exactly the same position. And without knowing the actual, exact
position of the other aircraft, a sudden departure from your steady, level
flight would make no sense. Which way would you go? How would you know that
you were flying away from the other aircraft, and not towards it? You would
have about a 50/50 chance.

I suppose I could have assumed that the Cessna was below me, and
climbed a 100', but I didn't.

And had you climbed and the Cessna been above you, that would be the end of
it.

Mxsmanic wrote in
news
Larry Dighera writes:

I considered maneuvering again, but finally
decided, that currently I was okay, and doing nothing would likely
not change that.

You did the logical thing. If you and the other aircraft had indeed
been in exactly the same position, you would have already collided.
Obviously you were not in exactly the same position. And without
knowing the actual, exact position of the other aircraft, a sudden
departure from your steady, level flight would make no sense. Which
way would you go? How would you know that you were flying away from
the other aircraft, and not towards it? You would have about a 50/50
chance.

I suppose I could have assumed that the Cessna was below me, and
climbed a 100', but I didn't.

And had you climbed and the Cessna been above you, that would be the
end of it.


If you had ever sat in a real Piper or a real Cessna, you would know that
it is safer for the Piper to climb than to descend. It is not a 50/50
proposition. But you don't fly and you're a moron.

Benjamin Dover writes:

If you had ever sat in a real Piper or a real Cessna, you would know that
it is safer for the Piper to climb than to descend.

Neither is safe if you do not have visual contact with the other traffic.

If neither aircraft has visual contact with the other, and no other
information is available, neither aircraft should take any special action. If
visual contact is available, the pilot(s) with contact should see and avoid.
If no visual contact has been made by either pilot, but one or both pilots has
other reliable sources of information allowing the aircraft to determine their
positions relative to each other, those sources can be used to determine what
action, if any, should be taken.

In this situation, it might help to share information on airspeed or DME from
the LAX VOR, either of which might help to locate the aircraft in relation to
each other. I suggest LAX because it's almost at right angles to the SFRA
route, whereas SMO would see both aircraft one behind the other. Of course,
if they are very close, DME might not be reliable.

I've wondered in the past exactly how aircraft coordinate their movements in
the SFRA, since the corridor in each direction is extremely narrow.