Final answer:
The number of display units (DUs) in the flight deck can vary depending on the aircraft's design. Modern commercial airliners typically have six primary display units, including the PFD, ND, and EICAS display.
Step-by-step explanation:
In the flight deck, the number of display units (DUs) can vary depending on the aircraft's design and configuration. One common layout is found in modern commercial airliners, such as the Boeing 737 or Airbus A320, which typically have six primary display units.These primary display units include the primary flight display (PFD), navigation display (ND), and engine indication and crew alerting system (EICAS) display.Additionally, there may be secondary displays like multifunction displays (MFDs), electronic flight bag (EFB) screens, or standby instruments. The exact number and arrangement of display units can differ based on the specific aircraft and its operator's preferences.