Low Vis, Low Speed Near Sea Level
Early in the “weather flying” series of posts, I discussed IIMC, or transitioning to the instruments when visual cues are lost, however, I did not address slow flight to avoid going IIMC. Although the MH-60T community is fortunate to fly a helicopter with a wide power margin near sea level, allowing pilots to get slow while still maintaining an ample power margin, when visibility comes down, in and around obstacles and terrain, pilots tend to still fly relatively fast (e.g., bucket airspeed or above – the community norm is no slower than 70 KIAS).
While there are some advantages to a 70 KIAS airspeed – above 50 KIAS the autopilot functions are all functioning (airspeed hold and coordinated turn) and pilots have the optimal power margin in the event of a loss of power, but there are two negative impacts of flying at this airspeed in low visibility conditions:
1. Pilots start to “out fly” their visibility (e.g., pilots are decreasing time available to identify and react appropriately to potential obstacles in the flight path).
2. Pilots are flying with a significant turn radius.
In very low visibility conditions, in and around terrain, near sea level, I have found that it is often best to be closer to 40 KIAS, which provides more time to identify, avoid, and mitigate obstacles and, in the event the crew determines it is best to turn around before IIMC, pilots can effect a safe course reversal by either coming into a hover and pedal turning, or by sliding and yawing into a tight, yet easy to manage, course reversal.
If the AOR includes areas where this would be useful (e.g., tight entrances to bays or river mouths), I recommend training an approach to the water and simulating entering these obstacle rich environments at a fast air taxi versus forward flight.
This technique can also increase safety margins in certain situations at altitude as well. However, pilots must be pay close attention to power requirements prior to the course reversal and recognize that this may not be an option with tight performance margins. Later on, I will cover initiating a hover for hoists at altitude in a series of posts dedicated to that subject.
