Left Pedal Awareness and LTE

Although the MH60T is a highly capable helicopter, it has two significant flaws, both of which become more pronounced during high power demands (slow flight and hovering) at altitude. 

1. The first “flaw” is TGT Limiting. As discussed at length in the previous two posts, pilots need to be exceptionally cognizant of their margins concerning power available and power required. If the power required exceeds the available power, most helicopters allow pilots to over-torque the transmission and/or over-temperature the engine in support of crew safety, though at the expense of additional aircraft maintenance costs. However, in helicopters operating the T700 series engine, once the engine reaches its temperature limit, it abruptly stops producing power. Even though the motors could generate more power, and the transmission could handle more torque, the limiter precludes this from happening. *** Note – in cold temperatures (starting between 0 and 10°C altitude dependent), the limit on power production of T700 engines changes from the TGT limiter to limitations associated with Ng. More on this later.   

2. The second “flaw” is its tail rotor. While the TGT limiting system is somewhat unique to helicopters powered by T700 series engines, tail rotor challenges are almost universal among helicopters. Compared to other model helicopters, the MH60T’s tail rotor performs well. Generally, the only loss of yaw control at low altitude, with a properly functioning tail rotor, is due to strong winds (or relative wind during fast sideward flight). In slow flight, strong crosswinds or tailwinds can result in a weathercocking phenomenon, where the nose of the helicopter snaps into the wind line regardless of pilot pedal input. Additionally, like other helicopters, when power required exceeds power available, as main and tail rotor speed decreases, pilots will lose directional control regardless of input. Of course, tail rotor malfunctions also include a loss of thrust or a stuck pedal/tail rotor pitch. The most insidious and frequent tail rotor issue in the Coast Guard H60s occurs at high altitude when a margin still exists between power available and power required, but the helicopter is operating near the edge of its performance limits, in which case, the tail rotor can run out of pitch and loose effectiveness. As student naval aviators, we studied the loss of tail rotor effectiveness. Granted, knowledge of the conditions that lead to LTE is relevant, in a general sense, for reducing risk through preventative measures. However, at altitude and in real time, a technical understanding of tail rotor aerodynamics will not typically aid pilots in determining how close they are to losing directional control, beyond understanding that high power requirements, high tail rotor pitch, and thin air will limit the available pitch remaining to overcome phenomena such as main rotor disk vortex interference or tail rotor vortex ring state. The only reliable, real-time indication of when a crew is on the verge of losing the ability to maintain directional control when they are hovering at altitude, near the edge of performance capability, is the amount of left pedal being used to keep heading constant, and how much remains before the pedal hits the stop. There have been several cases at high pressure altitudes where MH-60T and J pilots have run out of left pedal/tail rotor pitch resulting in an uncommanded right yaw. As such, CG H60 pilots must be aware of large amounts of left pedal during a constant heading hover.  Aside from narrow power margins, it is difficult to predict when pilots will run out of left pedal, at altitude, until they are in a hover. Therefore, during wind and terrain analysis and real time validation of power requirements in power limited situations, left pedal remaining should be considered just as important as the helicopter’s power margin. As power margins decrease and left pedal increases, a “down and right” escape for the helicopter in the event of an uncommanded right yaw must be considered and harnessed when feasible.   

Airbus, which has expended  significant resources studying LTE, has convincing data that many LTE related accidents are caused by pilots trying to fly out of uncommanded yaw in close vicinity to the ground or obstacles when they do not have ample separation, resulting in an aircraft strike from an otherwise recoverable situation. If operations require a helicopter to hover without an open area to “escape” down and right, Airbus emphasizes that it is best to maintain position with full left pedal and a slight, smooth lowering of the collective if altitude permits. Since the Coast Guard H60 community does not have a documented LTE procedure, below is a list of my personal LTE response steps comprised from research of other communities’ procedures and the lessons I have learned from others’ accounts:  

1. Full left pedal.  

2. Altitude permitting, lower the collective (as smoothly and minimally as the situation allows – recognizing that large rates of descent create a lot of inertia, which in turn creates a large power requirement to overcome, potentially exacerbating the situation particularly narrow power margins).  

3. Forward cyclic (obstacles permitting).