2012-11-19 According to a Lockheed Martin Press Release:
An F-35A Lightning II conventional takeoff and landing (CTOL) aircraft rapidly expanded its high angle of attack (AOA) test envelope to its 50 degree limit in only four flights during recent flight testing here.
F-35A test aircraft are limited to AOAs of 20 degrees until their controllability is proven at a higher AOA limit of 50 degrees.
The ability to rapidly progress to the maximum AOA indicates a sound aerodynamic and flight control system design.
High AOA testing will continue on the F-35A for several months testing the capabilities of all design loadings and the flight control system.
As one source has indicated about such testing:
Controlled flight at high angles of attack (AOAs) provides a modern fighter aircraft with the ability to turn rapidly, providing enhanced nose-pointing capability. The ability to accurately point the nose of the aircraft in a timely manner is the basis for handling qualities criteria and ratings.
Patrick C. Stoliker and John T. Bosworth, Evaluation of High-Angle-of-Attack
Handling Qualities for the X-31A Using Standard Evaluation Maneuvers (NASA, 1996).
And as a 1991 Air Force Test Pilot School Report noted:
From the designer to the pilot, everyone associated with the flying qualities of high performance military aircraft, particularly the fighter or attack variety, is or should be aware of the importance of the high angle of attack flight regime. It is here that the aircraft will spend a significant amount of its time when performing the mission for which it was designed. It is here that the aircraft must display its most outstanding performance.
It is also here that the aircraft, when pushed beyond its limits of controllability, can seemingly defy all laws of physics and principles of flight with which its surprised and often bewildered pilot is acquainted. The frequency of inadvertent loss of control at high angle of attack is such that many combat aircraft pilots are becoming firmly convinced that all pilots may be divided into two categories: those who have departed controlled flight, and those who will. Most thoroughly convinced are those pilots who fall into the former category. The unfortunate fact concerning departure from controlled flight at high angle of attack is that many aircraft and pilots are lost each year due to failure to recover from the out-of-control flight condition.
The circumstances surrounding the losses are varied. Departures from controlled flight may occur unintentionally during high-g maneuvers or intentionally during a nose-high deceleration to zero airspeed in an attempt to gain an advantage over an opponent in combat maneuvering; the aircraft may spin and the gyration be identified too late for recovery or a steep spiral may be mistakenly identified as a spin, causing recovery controls to be misapplied. Whatever the circumstances, departures from controlled flight result all too often in catastrophe. For this reason, test pilots in particular must be familiar with every facet of the high angle-of-attack flight regime.