Evaluation flight Heavy Attack Fighter F-16 block 52+ by USAF pilot. Watch the G counter on the top left of the HUD. Aircraft in particular exert g-forces on the axis aligned with the spine. This causes significant variation in blood pressure along the length of the subjects body and this limits the maximum g-forces that can be tolerated.

One often hears the term being applied to the limits that the human body can withstand without losing consciousness, sometimes referred to as "blacking out", or g-loc (loc stands for loss of consciousness).

A typical person can handle about 5 g (50m/s2) before this occurs, but through the combination of special g-suits and efforts to strain muscles —both of which act to force blood back into the brain— modern pilots can typically handle 9 g (90 m/s2) sustained (for a period of time) or more. Resistance to "negative" or upward gees which drive blood to the head, is much less. This limit is typically in the -2 to -3 g (-20 m/s2 to -30 m/s2) range. The vision goes red and is also referred to as a red out. This is probably due to capillaries in the eyes bursting under the increased blood pressure. Humans can survive about 20 to 40 g instantaneously (for a very short period of time). Any exposure to around 100 g or more, even if momentary, is likely to be lethal, although the record is 178 g.

The human body is considerably more able to survive g-forces that are perpendicular to the spine. In general when the acceleration pushes the body backwards (colloquially known as 'eyeballs in') a much higher tolerance is shown than when acceleration is pushing the body forwards ('eyeballs out') since blood vessels in the retina appear more sensitive to that direction.

Early experiments showed that untrained humans were able to tolerate 17 g eyeballs-in (compared to 12 g eyeballs-out) for several minutes without loss of consciousness or apparent long-term harm.

The F-16 Fighting Falcon is a multi-role jet fighter aircraft developed by General Dynamics in the United States. Designed as a lightweight fighter, it evolved into a successful multi-role aircraft. The Falcon's versatility is a paramount reason it was a success on the export market, serving 24 countries. The F-16 is the largest and probably most significant current Western fighter program, with over 4,000 aircraft built since production started in 1976. Though no longer produced for the United States Air Force, it is still produced for export.

The Fighting Falcon is regarded as a superb dogfighter, with innovations including a frameless canopy for better visibility, side-mounted control stick to ease control while under high g-forces, and reclined seat to reduce the effect of g-forces on the pilot. It was also the first fighter aircraft to be deliberately built to sustain 9g turns. It is also one of the few jets with a thrust-to-weight ratio greater than one, giving the Falcon excellent acceleration.In 1993 General Dynamics sold its aircraft manufacturing business to the Lockheed Corporation, which in turn became part of Lockheed Martin after a 1995 merger with Martin Marietta.Block 50/52 Plus (F-16U) Ordered by Polish Air Force. These aircraft are fitted with the latest avionics (including the ALE-50 Towed Decoy System) and provisions for Conformal Fuel Tanks (CFTs). On 9 November, 2006, it was unveiled that the Polish F-16s will be named Jastrzab (Hawk). Limited operational readiness will be achieved in 2008 and last F16 should be delivered by 2012. The Hellenic Air Force ordered this version with the CFTs. All two-seat "Plus" airframes include the enlarged Avionics Dorsal Spine which adds 30 cubic feet (850 L) to the airframe for more avionics with only small increases in weight and drag. This version is sometimes called F-16U and is the foundation of F-16E/F Block 60.[citation needed] The Republic of Singapore Air Force (RSAF) also ordered two-seat versions of the Block 52+. Singapore's most recent order consists of an aircraft model rumored to be the exact same configuration as the venerable F-16I, but re-designated to avoid sensitivity. The latest D+ models ordered by the RSAF can be noted to have the exact same antennas, sensor locations, cockpit configurations as that of the F-16I. These planes are also fitted with DASH-3 Helmet-mouted sighting system, 600-Gallon tanks, CFTs, AMRAAM, HARM and laser-guided weapons, fully-configured for long-range strike. The Pakistan Air Force ordered 18 Block 52 Plus F-16s with an option for 18 more as part of a $5.1 arms package. Pakistani F-16s will be equipped with AIM-120C5 AMRAAM, AIM-9M-8/9, JDAM, Harpoon Block II, Joint-Helmet Mounted Cueing System, CFTs and possibly IRIS-T.