Final answer:
If IR 1 failed or was turned OFF on the Captain's PFD, critical information such as heading, attitude, and airspeed may be missing or degraded, compromising situational awareness and potentially aircraft control.
Step-by-step explanation:
If IR 1 (Inertial Reference Unit 1) failed or was turned OFF on the Captain's Primary Flight Display (PFD) in an aircraft, several elements associated with attitude and navigation could be missing or degraded. These elements may include heading, attitude, and airspeed information, which are critical for maintaining situational awareness and aircraft control. The Captain's PFD relies on data from multiple systems, but principally from inertial reference units that provide information about the plane's movement and orientation. Without IR 1, redundancy may be compromised, and the Captain would have to rely more heavily on the second inertial reference system, IR 2, or other systems such as the air data computer, for vital flight information.
If the IR 1 (Infra-Red 1) fails or is turned OFF on the Captain's PFD (Primary Flight Display), there would be a few things missing. IR 1 is responsible for providing information on terrain and obstacles, so the terrain and obstacle data would no longer be displayed. Additionally, certain weather-related information, such as infrared satellite images, may also be missing.