BY ORDER OF THE SECRETARY OF THE AIR FORCE AIR FORCE ...

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AFMAN 11-217V1 3 JANUARY 2005
relatively narrow runway may give the illusion of being high. With an awareness of
these illusions under unlimited visibility conditions, it becomes easy to appreciate a
pilot's problems in a landing situation in which the approach lights and runway lights are
the only visual cues available.
15.2.2. No Vertical Guidance. Instrument approach lights do not provide adequate
vertical guidance to the pilot during low visibility instrument approaches. In poor
visibility, especially when the runway surface is not visible, or in good visibility at night,
there simply are not enough visual cues available to adequately determine vertical
position or vertical motion. Studies have shown that the sudden appearance of runway
lights when the aircraft is at or near minimums in conditions of limited visibility often
gives the pilot the illusion of being high. They have also shown that when the approach
lights become visible, pilots tend to abandon the established glide path, ignore their flight
instruments and instead rely on the poor visual cues. Another similar situation occurs
when a pilot flies into ground fog from above. If the pilot initially sees the runway or
approach lights, these cues will tend to disappear as the pilot enters the fog bank. The
loss of these visual cues will often induce the illusion or sensation of climbing. These
situations of erroneous visual cues convincing the pilot that the aircraft is above normal
glide path generally result in a pushover reaction, an increase in the rate of descent, and a
short or hard landing.
15.2.3. Descent Rate. Since approach lights are usually sighted close to the ground in
limited visibility, an increase in the rate of descent during the final approach when the
aircraft is very close to the ground may create a situation in which sufficient lift cannot be
generated to break the rate of descent when the pilot realizes he or she will land short.
15.2.4. Crosscheck. A recommended method to ensure against a dangerously high rate
of descent and a short or hard landing is to maintain continuous crosscheck of the GSI or
flight director and pay continuous attention to PAR controller instructions as well as VVI
and ADI indications. The pilot should establish predetermined limitations on maximum
rates of descent for the aircraft that he or she will accept when landing out of a low
visibility approach. Exceeding these limits during the transition to landing should result
in a go-around and missed approach in the interest of aircraft and aircrew safety.
Knowing that visual cues can be extremely erroneous, the pilot must continue to
crosscheck instruments and listen to the PAR controller's advisories even after runway
and/or approach lights have come into view. Most pilots find it extremely difficult to
continue to crosscheck their flight instruments once the transition to the visual segment
has been made, as their natural tendency is to believe the accuracy of what they are
seeing, or they continue to look outside in an effort to gain more visual cues. To
successfully continue reference to VVI and/or GSI when approach lights come into view,
a scan for outside references should be incorporated into the crosscheck at an early stage
of the approach, even though restrictions to visibility may preclude the pilot from seeing
any visual cues. If such a scan is developed into the crosscheck, it will facilitate the
recheck of flight instruments for reassurances of glide path orientation once visual cues
come into view and the visual transition is begun. See Chapter 20 for crosscheck and
landing considerations for those aircraft equipped with a Head-Up Display (HUD). The
following information deals with some of the conditions you may encounter during this
phase of flight.