There's two parts to the question... where I address in my document Distortion of Fact.
A critical component of airframe survivability while manoeuvring is how much g-force is applied. During a turn, g-force is the force that pushes you to the outside of the circle, such as how you will tend to lean to one side as you make a sharp turn in a car. The tighter and faster the turn, the higher the g-forces. 1 g is equal to the force of earth’s gravity. So at 4 gs everything will feel four times as heavy.
Aircraft designed for high-g manoeuvres such as fighter aircraft have to be made very strong, otherwise the forces acting on them can tear them apart.
The g-forces applied to AA77 during its descending turn can be calculated fairly easily using a simple formula:
A = v2 / r
Where r = the radius of the turn and v = velocity during the turn.
As previously stated, AA77’s turn was approximately 8km across, and the turn was completed at around 300KT. As the speed varied somewhat we will use a higher value of 350KT. A higher velocity will result in higher g-forces.
Converting to international units we get a velocity of 180ms-1 and a radius of 4,000m.
A = (180x180) / 4,000
A = 8.1
A represents the constant acceleration that the turning object experiences due to centripetal force.
Acceleration due to gravity is 9.8ms2, thus we can determine that the average lateral g-forces experienced by AA77 during the descending turn were 0.82 gs.
-Gumboot
A minor, minor, minor nitpick. Although the
lateral acceleration might have been .82 g, the airplane and the passengers wouldn't have experienced the forces as lateral forces. (They wouldn't be thrown to the side at .82 g) Because the airplane is banked, and in coordinated flight, they would have just been pushed down into their seats a little more. Due to the nature of vector addition, the result is not 1.82 g.
The easiest way to calculate this is to take 1 divided by the cosine of the bank angle.
So, for 20 degrees, 1.06 g. 30 degrees, 1.15 g. 41 degrees, 1.32 g.
If the pilot had taken it up to 60 degrees of bank (the onset of what the FAA determines to be aerobatic flight), it would have been 2 g.
These are steady state values, you could vary them a little momentarily by pushing or pulling on the stick.
I figure you probably already know this.
It's also worth pointing out that a "standard rate turn", marked on the turn coordinator, makes a 360 degree turn in two minutes. That's 3 degrees per second.
330 degrees/198 seconds is less than two degrees per second, so rather than being an abrupt aerobatic maneuver, it was actually a fairly bland turn, not inconsistent with a pilot who would like to nail the standard rate, but isn't comfortable with high bank angles, and then has to go to even higher bank angles to get things lined up again.