Expedient Pre-Launch Planning for Time-Sensitive Power-Limited Missions

Over the past six years, I have been working in Alaska and the Pacific Northwest where units execute “inland” missions more frequently than other Coast Guard rotary-wing units. My primary responsibility in most of these missions was as the “ops call taker,” receiving requests for assistance, assessing feasibility, and collaborating with ground responders and helicopter crews to enhance safety and optimize rescue operations. 

In Alaska, “inland” cases tended to be below 6000’. In contrast, the Pacific Northwest is conducive to high altitude “inland” rescue missions. Central Oregon and Washington both have airports and fuel within 20 nautical miles of numerous high Cascade Range peaks. Additionally, the climate in central Oregon is generally dry, with weather conditions favorable for helicopter response. In some cases, there are tops above mountain obscuration. On more than one occasion, Oregon crews launched IFR, flew above the cloud tops, hoisted at altitude with excellent visibility, and then recovered IFR back down through the clouds. These were some of my most enjoyable missions because they combine two of the Coast Guard rotary-wing community’s strengths: weather flying and hoisting.  

During my tenure managing CG helicopter operations in Astoria, Oregon, the unit received a substantial volume (for a CG unit) of requests for high-altitude hoisting. I estimate we processed over 30 responses annually, in collaboration with our Pacific Northwest “inland” SAR partners, most which pushed the limits of the MH60-T helicopter’s capabilities. As a collective response team, we identified alternative rescue options, due to adverse weather conditions or insufficient performance to hover for a hoist, in about half of the cases. The remaining half of the cases required a response with varying degrees of helicopter performance margins. 

If a time-sensitive case necessitates a helicopter hover with narrow performance margins, swiftly and accurately determining the required performance specifications is paramount. Consequently, I advise against using the legacy method performance planning method because the traditional methods of TOLD calculations are cumbersome, time-consuming, and susceptible to human error.  

Instead, I prefer to plan hover performance using cruise charts, which provide an immediate maximum torque available (MTA), intermediate torque available (ITA), and continuous torque available (CTA). While the granularity of the data is slightly reduced due to the cruise charts’ 10° and 2000’ increments, pilots can still rapidly interpolate and achieve an accuracy within a percentage point of legacy methods. In seconds, pilots can compare the power required to hover out of ground effect (HOGE) at various weights to the power available. 

In addition to the efficiency and clarity provided by comparing different weights and HOGE values to the available power, pilots also can account for wind in a hover on cruise charts (without relying on less accurate extrapolated numbers that accompany our hover performance charts). Because of these attributes, this technique is an essential element of airmanship every CG pilot should master before embarking on a short-notice, high-altitude launch. Moreover, harnessing this technique has significantly improved the accuracy and efficiency of my performance planning near sea level, and during performance evaluations we conduct annually. 

This technique is illustrated with a specific example of a hoist mission at approximately 6,000’ and a 10°C cruise chart.  

Referencing the 6,000’ PA 10°chart, we can immediately determine that our ITA (where Nr would droop with our contingency power off) is 107%. The 30 minute threshold is 98%, and CTA (also known as max continuous power/MCP) is 90% with ECS on.  

*** Note that the power values for the 30-timer and CTA/MCP on the cruise charts is with ECS on. If pilots are deriving CTA/MCP from the engine performance charts, those values are with ECS off. This will result in a slightly lower CTA/MCP value on the cruise charts compared to the engine performance charts. 

To determine MTA on the cruise chart (6000’ PA, 10°C), pilots simply double the value at the bottom of the line labeled “SE 2.5 MIN.” Therefore, the MTA in a hover (with 1.0 engines) will be 110% (The SE 2.5 min line represents the power of one engine producing 110%). 

At a pressure altitude of 6000’ and an outside air temperature of 10°C: MTA = 110% ITA = 107% 30 minute power = 98% (ECS on) CTA/MCP = 90% (ECS on) 

Once power available is determined, pilots can refer to the bottom of the cruise chart to determine power required to HOGE values at different weights. 

At 20,000 lbs. (approximately 4,000 lbs. of fuel with a standard MH60T configuration and SAR crew), the OGE is about 105%. 

At 18,000 lbs. (approximately 2,000 lbs. of fuel with a standard MH60T configuration and SAR crew), the OGE is about 89%. 

Interpolating between the 18,000 and 20,000 lines, pilots can estimate that at 19,000 lbs. (approximately 3,000 lbs. of fuel with a standard MH60T configuration and SAR crew), the OGE is about 97%. 

*** Note that there is a 16% OGE spread between 18,000 and 20,000 (8% per 1,000 lbs.). The 6% per 1,000’ rule of thumb is quite general and more accurate at sea level. I will discuss this further when I delve into the role of tab data in mission planning. 

Within a minute, pilots can calculate a 10% power margin between the OGE power required and the MTA power available (contingency power is 110%). This means that HOGE is approximately 100%, which equates to about 19,400 lbs. (roughly 3,400 lbs.) of fuel. 

To determine power requirements in ground effect, go to the hover chart, find the HOGE torque value per engine and move right across the chart to the appropriate wheel height. If pilots are planning on a HOGE of 100%, a 10’ HIGE would require 84%; a 20’ HIGE would require 92%. During a HOGE of 85%, these values would be 72% and 78%, respectively (no temperature, pressure altitude, and weight is necessary for this evaluation making it more simple and less prone to error).  

For high altitude missions requiring accurate and efficient performance planning, using cruise charts to make power calculations not only mitigates risk, but enhances case management and mission planning before departure (e.g., fuel load and other weight considerations), as well as in flight (fuel management, performance management, wind and environmental considerations, etc.). For cases closer to sea-level, this method offers a more efficient alternative, or quality assurance, in near sea-level operations, and aids in acing the performance challenges during the annual STAN evaluation. 

Two final comments:  

The indicated airspeed axis on the cruise charts can be used to determine the effect of wind on power available in a HOGE. For example, at 6000’ pressure altitude, and 10°C with a gross weight of 20,000 lbs., no wind HOGE power required will be 105%. 10 knots of wind will decrease this value to 98%; 20 knots of wind will decrease the value to 81%.  

The data from the cruise charts is referenced by the MH-60T avionics suite to determine the performance values pilots’ harness in flight. For example, the hover override page in the CDU (accessed by the TDL button) provides crews HOGE power required data derived from the cruise charts (the way I suggest we conduct performance planning in this post).