Engine Start and Rotor Engagement Rotor Safety Considerations The use of an MEL for rotorcraft operated under part 91 also  allows for the deferral of inoperative items or equipment. The  primary guidance becomes the FAA-approved MEL issued  to that specific operator and N-numbered helicopter. During the engine start, rotor engagement, and systems  ground check, use the manufacturer’s checklists. If a problem  arises, have it checked before continuing. Prior to performing  these tasks, however, make sure the area around and above  the helicopter is clear of personnel and equipment. Position  the rotor blades so that they are not aligned with the fuselage.  This may prevent the engine from being started with the  blades still fastened. For a two-bladed rotor system, position  the blades so that they are perpendicular to the fuselage  and easily seen from the cockpit. Helicopters are safe and  efficient flying machines as long as they are operated within  the parameters established by the manufacturer. The FAA has developed master minimum equipment lists  (MMELs) for rotorcraft in current use. Upon written request  by a rotorcraft operator, the local FAA Flight Standards  District Office (FSDO) may issue the appropriate make and  model MMEL, along with an LOA, and the preamble. The  operator then develops operations and maintenance (O&M)  procedures from the MMEL. This MMEL with O&M  procedures now becomes the operator’s MEL. The MEL,  LOA, preamble, and procedures document developed by the  operator must be on board the helicopter when it is operated. The FAA considers an approved MEL to be a supplemental  type certificate (STC) issued to an aircraft by serial number  and registration number. It therefore becomes the authority  to operate that aircraft in a condition other than originally  type certificated. The exposed nature of the main and tail rotors deserves  special caution. Exercise extreme care when taxiing near  hangars or obstructions since the distance between the  rotor blade tips and obstructions is very difficult to judge.  [Figure 8-2]  In addition, the tail rotor of some helicopters  cannot be seen from the cabin. Therefore, when hovering  backward or turning in those helicopters, allow plenty of  room for tail rotor clearance. It is a good practice to glance  over your shoulder to maintain this clearance With an approved MEL, if the position lights were discovered  inoperative prior to a daytime flight, the pilot would make  an entry in the maintenance record or discrepancy record  provided for that purpose. The item is then either repaired or  deferred in accordance with the MEL. Upon confirming that  daytime flight with inoperative position lights is acceptable in  accordance with the provisions of the MEL, the pilot would  leave the position lights switch  off , open the circuit breaker  (or whatever action is called for in the procedures document),  and placard the position light switch as INOPERATIVE. Another rotor safety consideration is the thrust a helicopter  generates. The main rotor system is capable of blowing sand,  dust, snow, ice, and water at high velocities for a significant  distance causing injury to nearby people and damage to  buildings, automobiles, and other aircraft. Loose snow, sand,  or soil can severely reduce visibility and obscure outside visual  references. There is also the possibility of sand and snow  being ingested into the engine intake, which can overwhelm  filters and cutoff air to the engine or allow unfiltered air into  the engine, leading to premature failure. Any airborne debris  near the helicopter can be ingested into the engine air intake  or struck by the main and tail rotor blades.  There are exceptions to the use of the MEL for deferral. For  example, should a component fail that is not listed in the  MEL as deferrable (the rotor tachometer, engine tachometer,  or cyclic trim, for example), then repairs are required to be  performed prior to departure. If maintenance or parts are not  readily available at that location, a special flight permit can  be obtained from the nearest FSDO. This permit allows the  helicopter to be flown to another location for maintenance.  This allows an aircraft that may not currently meet applicable  airworthiness requirements, but is capable of safe flight, to  be operated under the restrictive special terms and conditions  attached to the special flight permit. Deferral of maintenance is not to be taken lightly, and due  consideration should be given to the effect an inoperative  component may have on the operation of a helicopter,  particularly if other items are inoperative. Further information  regarding MELs and operations with inoperative equipment  can be found in AC 9 1-67, Minimum Equipment Requirements  for General Aviation Operations Under FAR Part 91. Figure 8-2.  Exercise extreme caution when hovering near buildings  or other aircraft. 8-3