"position & hold" going away

"Matt Whiting" wrote in message
...

No, I meant give the takeoff clearance a little sooner while the aircraft
that just landed is still going down the runway heading for the taxiway.
This would have the same advantage as P&H in most circumstances.


That has the disadvantage of not ensuring runway separation.



Yes, that works also, but then what is the point of P&H if not to get more
throughput per active runway?


The point of position and hold IS to get more throughput per active runway,
and it does. Withholding the landing clearance while an aircraft is in
position wouldn't change that. Right now, aircraft can be cleared to land
while a departing aircraft is in position on the runway. Obviously, some
action has to be taken before the arriving aircraft can land safely, the
controller expects to issue a takeoff clearance to the aircraft in position
before the arriving aircraft gets too close. But what if he doesn't for
some reason?

"peter" wrote in message
oups.com...

The accident happened shortly before sunset on runway 24. So the
pilots on the 737 would have been looking nearly into the sun whereas a
pilot looking back would be seeing a landing light in a darkening sky.


How is it that they were able to see the runway but not an airplane of 95'
wingspan and 82' length sitting on it? Why would a pilot looking back see a
landing light in a darkening sky if the sun was brightly shining on the
approaching airplane? You can't have it both ways.

When I find the sun shining in my eyes like that I adjust my visor.



But regardless of the details of this particular incident, why not have
the redundancy of having both aircraft crews in a position where they
could observe and possibly avert an imminent collision?


That would require the airplane in position to turn towards approaching
aircraft and defeat the purpose of position and hold.

How is it that they were able to see the runway but not an airplane of 95'
wingspan and 82' length sitting on it?

I don't know; I wasn't there. But it doesn't seem unreasonable to me
that an airplane could appear to blend into the runway under certain
conditions, that being one of them. Granted, they could "see" the
airplane, inasmuch as photons reflected from the plane entered the eye.
However, it might not have been recognized as an airplane if the
contrast were low enough, there was enough glare, the pilots were
focused on ("fixated on?") some other aspect of the approach (maybe the
theshold markings, the far end, the sight picture...) It would clearly
be pilot error, but it's possible for pilots to =make= errors, even
experienced ones.

Why would a pilot looking back see a
landing light in a darkening sky if the sun was brightly shining on the
approaching airplane?

That depends on the albedo of the airplane, the angle it presented to
the sun, the brightness of the landing light, and the exact direction it
was facing. It does not sound unreasonable to me, although I wasn't
there at that exact moment.

Jose
--
Quantum Mechanics is like this: God =does= play dice with the universe,
except there's no God, and there's no dice. And maybe there's no universe.
for Email, make the obvious change in the address.

The accident happened shortly before sunset on runway 24. So the
pilots on the 737 would have been looking nearly into the sun whereas a
pilot looking back would be seeing a landing light in a darkening sky.

How is it that they were able to see the runway but not an airplane of 95'
wingspan and 82' length sitting on it?

Because they were human and sometimes make mistakes, especially under
conditions of poor visibility such as caused by having to look in the
direction of the sun near the horizon.

Why would a pilot looking back see a
landing light in a darkening sky if the sun was brightly shining on the
approaching airplane? You can't have it both ways.

Go out just before sunset and look at the sky in the direction opposite
from the sun. You should notice that it's already considerably darker
than at midday even though the sun has not yet set. Looking in that
direction a plane would be very easy to see because it would be
brightly lit by the sun and is set against a darker background sky. If
the landing light is on that would make it even more visible.

So at the time of this accident the crew of the landing plane had
relatively poor visual conditions while if the crew of the plane on the
ground had been in a position to look back they would have had
excellent visibility.

When I find the sun shining in my eyes like that I adjust my visor.

That helps but certainly doesn't fully eliminate the problem.

But regardless of the details of this particular incident, why not have
the redundancy of having both aircraft crews in a position where they
could observe and possibly avert an imminent collision?

That would require the airplane in position to turn towards approaching
aircraft and defeat the purpose of position and hold.

Presumably the purpose is to be able to respond quickly to a clearance
to take off. If the plane is angled but full power can still be
applied and the plane's path down the runway straightened out in the
first few seconds of the takeoff roll then no time would be lost and
the same purpose would still be achieved.

How is it that they were able to see the runway but not an airplane of 95'
wingspan and 82' length sitting on it?

People see what they expect to see. Same with hearing what they expect
to hear. Radio clearances have readbacks to protect against this, and
visual stuff have co-pilots to be a second opinion, but sometimes the
system breaks down. In this case, it broke down terribly.

Ben Hallert
PP-ASEL

Ben wrote:
How is it that they were able to see the runway but not an airplane of 95'
wingspan and 82' length sitting on it?

People see what they expect to see.

Yes. An interesting illustration of that was provided in the
psychology study that showed a film of a group passing basketballs back
and forth. The audience was asked to watch the film and count the
number of passes between members of the white-shirted team. After the
one minute film the audience was asked to write down the number of
passes and anything unusual they may have noticed during the film.
Less than half commented on the fact that toward the middle of the clip
a large man in a gorilla costume walked across the room, stood right in
front of the camera and beat his chest and then slowly walked back out.
See http://apps.carleton.edu/voice/features.php3?id=106

When our attention is focussed on one aspect of a scene it's very easy
to ignore everything else.

Most of the near collisions on the runway that I am aware of have
involved aircraft that were either both taking off or both were landing.

"Jose" wrote in message
t...

I don't know; I wasn't there. But it doesn't seem unreasonable to me that
an airplane could appear to blend into the runway under certain
conditions, that being one of them. Granted, they could "see" the
airplane, inasmuch as photons reflected from the plane entered the eye.
However, it might not have been recognized as an airplane if the contrast
were low enough, there was enough glare, the pilots were focused on
("fixated on?") some other aspect of the approach (maybe the theshold
markings, the far end, the sight picture...) It would clearly be pilot
error, but it's possible for pilots to =make= errors, even experienced
ones.


Well, if the conditions are such that the arriving aircraft cannot see an
aircraft on the runway, it's unlikely the aircraft on the runway could have
spotted the arriving aircraft even if it had been cocked towards it. The
aircraft on the runway has to scan a larger area and at varying distances.
The arriving aircraft has to scan a much smaller area and at a fixed
distance, the runway surface.



That depends on the albedo of the airplane, the angle it presented to the
sun, the brightness of the landing light, and the exact direction it was
facing. It does not sound unreasonable to me, although I wasn't there at
that exact moment.


The landing light may have made the arriving aircraft harder to spot. In
WWII it was found that forward facing lights mounted on ASW aircraft allowed
them to get closer to surfaced submarines before being spotted.

"peter" wrote in message
ups.com...

Because they were human and sometimes make mistakes, especially under
conditions of poor visibility such as caused by having to look in the
direction of the sun near the horizon.


Why would they be looking in the direction of the sun near the horizon
instead of in the direction of the runway?



Go out just before sunset and look at the sky in the direction opposite
from the sun. You should notice that it's already considerably darker
than at midday even though the sun has not yet set. Looking in that
direction a plane would be very easy to see because it would be
brightly lit by the sun and is set against a darker background sky. If
the landing light is on that would make it even more visible.

So at the time of this accident the crew of the landing plane had
relatively poor visual conditions while if the crew of the plane on the
ground had been in a position to look back they would have had
excellent visibility.


If it's truly just before sunset there isn't much sun above the horizon to
be shining in the eyes of the approaching crew.



Presumably the purpose is to be able to respond quickly to a clearance
to take off. If the plane is angled but full power can still be
applied and the plane's path down the runway straightened out in the
first few seconds of the takeoff roll then no time would be lost and
the same purpose would still be achieved.


Time is lost because full power is not being applied in the direction of the
takeoff roll.

"Ben Hallert" wrote in message
oups.com...

People see what they expect to see.


A pilot sitting on a runway obviously wouldn't expect to see an airplane
landing on that runway.