the external scene by use of an imaging sensor, such as  a Forward-Looking InfraRed (FLIR) or millimeter wave  radar (MMWR). In 2004, 14 CFR part 91, section 91.175  was amended to reflect that operators conducting straight- in instrument approach procedures (in other than Category  II or Category III operations) may now operate below the  published decision height (DH) or minimum descent altitude  (MDA) when using an approved EFVS shown on the pilot’s  HUD. This rule change provides “operational credit” for EV  equipage. No such credit exists for SV.  This chapter provides an introduction to aeromedical factors  relating to flight activities. More detailed information on  the subjects discussed in this chapter is available in the  Aeronautical Information Manual (AIM) and online at www.  faa.gov.  Chapter Summary  17-29 