Holding patterns - are they a macro or actually tracked?


#1

Hi,

I was on Virgin Australia flight VA341 yesterday departing Melbourne YMML arriving Brisbane YBBN.
flightaware.com/live/flight/VOZ3 … /YMML/YBBN

While Brisbane airport can have approach delays requiring a holding pattern, my surprise was that the holding pattern we had showed a left turn when the plane very distinctly felt like it banked RIGHT… (ie the right side of the plane lower and the left side higher).

I know the turn I felt was directly related to the holding pattern and not another part of the flight as
a) it coincided with the pilot announcement approx 1910 of delayed arrival 1930
b) the bank was not a subtle correction but steep enough to be a smooth turn and lasted between 30seconds-60seconds.
c) the flight track graph shows the directional changes corresponding to the times.

My first reaction to seeing the recorded path is that a holding pattern might be a macro/shortcut generated flight plan that due to some kind of data entry error mismatched the left/right turn information.
Does that happen? I imagine not, I assume that its all just tracking data points joined.

Since the track data records N, NW, W, SW, SW directional changes, both the visual plot and the numerical plot indicate a left turn.

Therefore I am primarily lead to the conclusion that I incorrectly experienced the turn, most likely due to a centrifugal force offsetting gravity. Normally I sense changes in inclination very well though!

I am a little at a loss to explain how a left turn could feel like a right bank though…

I was curious if anyone had thoughts on the subject?

Cheers,
David


#2

Here is a really good article from the FAA on spatial disorientation. Were you able to look outside (see the ground) when the turn was happening?

faa.gov/pilots/safety/pilots … atialD.pdf


#3

Many thanks CaptainK727!

Yes you were right to ask about visual reference - at the time I had no visual reference at all.

I now believe I experienced the following, excerpted pages 2-4 from the document you linked, particularly my underlined part…:

[quote=“FAA faa.gov/pilots/safety/pilots … atialD.pdf”]
The Semicircular Canals
The semicircular canals are three half-circular, interconnected tubes located inside each ear that are the equivalent of three gyroscopes located in three
planes perpendicular (at right angles) to each other. Each plane corresponds
to the rolling, pitching, or yawing motions of an aircraft.

Each canal is filled with a fluid called endolymph and contains a motion
sensor with little hairs whose ends are embedded in a gelatinous structure
called the cupula. The cupula and the hairs move as the fluid moves inside the
canal in response to an angular acceleration.

The movement of the hairs is similar to the movement of seaweed caused
by ocean currents or that of wheat fields moved by wind gusts. When the
head is still and the airplane is straight and level, the fluid in the canals does
not move and the hairs stand straight up, indicating to the brain that there is
no rotational acceleration (a turn).

If you turn either your aircraft or your head, the canal moves with your head, but
the fluid inside does not move because of its inertia. As the canal moves, the hairs
inside also move with it and are bent in the opposite direction of the acceleration by
the stationary fluid (A). This hair movement sends a signal to the brain to indicate
that the head has turned. The problem starts when you continue turning your aircraft at a constant rate (as in a coordinated turn) for more than 20 seconds.

In this kind of turn, the fluid inside the canal starts moving initially, then
friction causes it to catch up with the walls of the rotating canal (B). When
this happens, the hairs inside the canal will return to their straight up position,
sending an erroneous signal to the brain that the turn has stopped–when, in
fact, the turn continues.
If you then start rolling out of the turn to go back to level flight, the fluid
inside the canal will continue to move (because of its inertia), and the hairs will
now move in the opposite direction ©, sending an erroneous signal to the brain
indicating that you are turning in the opposite direction, when in fact, you are
actually slowing down from the original turn.

Vestibular Illusions
(Somatogyral - Semicircular Canals)

Illusions involving the semicircular canals of the vestibular system occur
primarily under conditions of unreliable or unavailable external visual references and result in false sensations of rotation. These include

  • the Leans,

  • the Graveyard Spin and Spiral, and

  • the Coriolis Illusion.

The Leans.
This is the most common illusion during flight and is caused
by a sudden return to level flight following a gradual and prolonged turn that
went unnoticed by the pilot.
The reason a pilot can be unaware of such
a gradual turn is that human exposure to a
rotational acceleration of 2 degrees per second or lower is below the detection threshold of the semicircular canals. Leveling the
wings after such a turn may cause an illusion
that the aircraft is banking in the opposite
direction. In response to such an illusion, a
pilot may lean in the direction of the original turn in a corrective attempt to regain the
perception of a correct vertical posture.

[/quote]


#4

While Brisbane airport can have approach delays requiring a holding pattern, my surprise was that the holding pattern we had showed a left turn when the plane very distinctly felt like it banked RIGHT… (ie the right side of the plane lower and the left side higher).

Coriolis effect?
science.howstuffworks.com/scienc … seball.htm

drains in the Northern Hemisphere always empty to the left (counterclockwise) and those in the Southern Hemisphere empty to the right (clockwise).

:wink:


#5

The lat/lon of all the position reports that resulted in the track map you saw are here: flightaware.com/live/flight/VOZ … N/tracklog


#6

drains in the Northern Hemisphere always empty to the left (counterclockwise) and those in the Southern Hemisphere empty to the right (clockwise).

:wink:

False - I learned that toilets drain in the direction the MFG picks, it was on Mythbusters…


#7

You didn’t forget the 4x effect, did you? :stuck_out_tongue:


#8

Hi thanks but in my original post I already acknowledged the track data…:

“c) the flight track graph shows the directional changes corresponding to the times.”

“Since the track data records N, NW, W, SW, SW directional changes, both the visual plot and the numerical plot indicate a left turn.”

Cheers
David


#9

LOL! No, there was zero 4x effect =)

CaptainK727 was right on the money, I experienced spatial disorientation and learned quite a bit from the experience.

Cheers everyone