SFAR 73 (2)(a) - Ground Training
Ground Training - previously Awareness Training
In accordance with SFAR 73 (2)(a), no person may manipulate the controls of a Robinson model R-22 or R-44, unless ground training specified in SFAR 73 (2)(a)(3) has been completed and that person's logbook has been endorsed by a flight instructor authorized under SFAR 73 (2)(b)(5)(iv).
SFAR 73 (2)(a)(3) states that the following ground training must be conducted by a flight instructor who has been authorized under SFAR 73 (2)(b)(5)(iv) and must consist of the following general subject areas (MELLR):
- Mast bumping
- Energy management
- Low rotor revolutions per minute (RPM) and rotor stall
- Low G conditions, effects, and proper recovery procedures
- Rotor RPM decay
The order of explanation does not coincide with the acronym MELLR, and is just a suggested order.
Low rotor revolutions per minute (RPM) and rotor stall
Low RPM blade stall is a unrecoverable condition that can occur at any airspeed, causing the main rotor to produce insufficient lift to keep the helicopter in the air. With lower RPMs, the rotor blades have to increase in pitch to produce adequate lift. This causes the blades to exceed their critical angle of attack which will lead to the blade stalling. A combination of insufficient RPMs, increased pitch angle and an increased descent rate will make it virtually impossible to recover. Low RPM blade stall can occur at 80% RPMs, plus 1% RPM for every 100 feet. Recovery is to lower collective and roll the throttle on.
Here's a link to Robinson's Safety Notice 24 - Low Rotor RPM Stall can be Fatal
Rotor RPM decay
Due to the nature of the R22's rotor system, in the event of an engine failure or a situation with low rotor RPMs, an increased pitch angle will rapidly decrease the rotor RPMs.
Energy management
As helicopter pilots we are constantly managing our aircraft's energies, whether it is potential (altitude), kinetic (airspeed) or rotational (RPMs) energy. In an emergency situation, say we have to enter an autorotation due to an engine failure, we can trade these energies to make it down to the ground safely.
| Phase | Potential | Kinetic | Rotational |
|---|---|---|---|
| Glide | Decreasing | Maintained | Maintained |
| Flare | Maintained | Decreasing | Maintained |
| Touchdown | Decreasing | Decreasing | Lift for touchdown |
Low G conditions, effects, and proper recovery procedures
Low G, or a condition of weightlessness, is a hazardous condition that can lead to loss of control over our helicopter and Mast bumping. We can get into a Low G condition via control inputs like a rapid forward cyclic movement, this is often referred to as a Low G pushover), or from turbulence. When we enter a Low G condition, we lose control authority of the helicopters direction of flight and due to our symmetrical stabilizer we can get a right or left roll. To recover from Low G we want to apply slight aft cyclic, to reload our rotor disk, and only once it has been reload should we apply lateral cyclic to correct any roll.
Mast bumping
Mast bumping is a catastrophic event where a helicopter with a teetering rotor system - like our R22 or R44 - exceeds operational limits of the rotor system causing the main rotor to separate from the main rotor mast. This happens due to excessive teetering, which can be caused by Low G or turbulence.
Endorsement example
I certify that [First Name, Last Name, Pilot Cert. No.______] has received the Ground Training required by SFAR 73 (2)(a)(3)(i-v). [CFI Name & Signature, Cert. No. & Expire date]