Flight Operations

Choosing the Right Helicopter -No Simple Decision

by Noel Preston

Aerospatiale's TwinStar, similar to the one operating for Flight for Life in Colorado Springs, is currently the most prolific twin-engine helicopter on U.S. hospital contracts.

More than one hundred and thirty hospitals have chosen helicopters for their aeromedical programs and put them in operation. With a collective aeromedical experience spanning several years, many of these hospitals are now considering a change in the type of helicopter they operate. Other hospitals are choosing a helicopter for initiation of an aeromedical program. Just how should an EMS helicopter be selected, and how simple is the selection process?

The goal in selecting a helicopter should be to identify the helicopter type which satisfies mission requirements in the safest, most efficient and economical manner. In doing so, this selection process should focus on the following areas:

1. Identify mission requirements: - Mission medical requirements definition - Mission operational requirements definition

2. Analyze characteristics of candidate helicopters:

- Helicopter performance capabilities. - Operator considerations

3. Financial considerations.

Mission medical requirements definition Mission medical requirements definition

should include answers to the following questions:

1. What will be the medical crew composition? In addition to a pilot, some

programs fly with a single flight nurse, others a doctor and flight nurse. Crew composition affects cabin layout and weight calculations for helicopter configuration, performance and fuel loading.

2. What medical equipment is required? What are the characteristics of that equipment with regard to weight, size, power requirements and "quick-change" capability?

3. How often will it be necessary to carry two patients simultaneously? Will one litter position suffice?

4. What is the required medical working area in terms of length, width and height?

Mission operational requirements definition

A definition of mission operational requirements should include answers to the following questions:

1. ls a single engine helicopter adequate, or is a multi-engine helicopter desired?

2. Is an Instrument Flight Rules (IFR) capability required? Even if IFR flight plans will not be flown, an IFR capability is a valuable safety tool for night flying or in the event that IMC (Instrument Meteorological Conditions) are inadvertently encountered.

3. What range capability is necessary? What range capability is desired? Range

calculations for helicopter comparisons should assume a fall load of medical personnel, equipment and patient(s). The possibility of unfavorable winds should also be considered. Adequate fuel reserves should be accounted for, and not applied to the range calculations. Generally, a helicopter's range varies with the weight of payload to be carried, and the speed at which it is flown. These variations are attributable to the necessity to trade off payload (weight) for fuel load, and speed for fuel rate consumption in order to keep within airframe and other performance limitations.

Figure 1 shows typical payload-range capabilities for five different aeromedical helicopter types under no-wind conditions. For example, differences are clear, as ranges for the different helicopters vary from 195 to 335 nautical miles with a payload of 875 pounds.

4. What density altitudes will be encountered, both in normal operations and under unusual circumstances? Density altitude is basically height above sea level corrected for temperature and, to a lesser degree, humidity. Helicopter performance capability decreases as density altitude increases, so operations at high elevations or high temperatures require special consideration.

5. Are there special equipment requirements, such as spotlights, or flotation equipment for flight over water? Most special equipment requirements carry weight and/or cost penalties.

8 HOSPITAL AVIATION, JULY 1986

Flight Operations

The BK-117 has grown faster in hospital ranks than any other helicopter. The first BK-117 on a U.S. hospital contract was flown by U.S. Jet Aviation for Washington Hospital Center in Washington, D.C. in 1983.

Bell has nearly doubled its fleet of 222UTs on aeromedical contracts during the past 12 months. University Medical Center in Salt Lake City has operated 222s for three years.

This Agusta 109, flying for North Memorial Air Care in Minneapolis, remains the fastest of all helicopters currently flying for hospitals in the United States.

Helicopter Performance Capabilities This area of analysis has a direct effect

on the safety potential of the heiicopter operation. Factors that should be considered include the following:

1. Hover out of ground effect performance, or HOGE. The random nature of aeromedical helicopter operations dictates that slow forward flight and/or high hovers may be necessary to clear obstructions or suitably inspect restricted landing areas. Analysis of different helicopters' capabilities should include recognition of the impact of high temperatures on altitude limits at which the helicopters can hover out of ground effect at full mission weight. Full mission weight assumes the following is aboard the helicopter:

- Full mission equipment - Full mission personnel, including patient(s) - Full mission fuel If a helicopter's HOGE ceiling is lower

than density altitudes which may be encountered, that helicopter won't accomplish all missions that may be required.

An example of how hover capabilities can vary among different helicopters is shown in Figure 2. HOGE ceilings were determined for five different helicopter models, all of which are presently in aeromedical service. Figure 2 shows that on a hot day, two of these would not be practical at elevations higher than 2,000 feet above sea level.

NOTE: Helicopter maximum gross weight is used for full mission weight for these comparison examples. Actual full mission weight for some programs may be less, in which case performance would be better.

2. Single engine climb performance. We don' t like them, but engine power losses do occur, often at times and places of Murphy's choosing. It's desireable that the helicopter be able to continue flight with one engine inoperative (OE1) at full mission weight, since we frequently fly over terrain that does not offer an immediate safe landing area. This comparison should analyze two areas, again based on full mission weight and mission density altitude:

- What is the OEI climb rate, assuming that the helicopter is flying faster than single engine safety speed at the time of failure? Figure 3 contains a comparison of OEI climb rates. Again we see that not all helicopters are created equal. - What is the rejected takeoff distance that guarantees a safe landback or continued flight if engine failure should occur during takeoff? Clearly the opt imum rejected takeoff distance is zero, as this offers the capability to fly away following engine failure at any point in the takeoff sequence. However, rejected takeoff distances for modern

10 HOSPITAL AVIATION, JULY 1986

Fl ight Opera t ions

twin engine helicopters at maximum gross weight can range from zero to more than 1,400 feet horizontally. Program administrators should be aware of the risk which this implies before putting their medical people in a helicopter which you select.

3. Cruise speed. Fast cruise speed has obvious value for EMS operations. Maximum cruise speeds can decrease significantly, however, as helicopter weight, density altitude and ambient temperatures increase. Again, when comparing helicopter cruise speeds, use the full mission weights which are anticipated for each helicopter, as well as the anticipated environmental conditions.

4. Dispatch reliability. Helicopters are machines and, like all machines, some are more reliable than others. If the machine won't go, all the good human intentions are for naught. Evaluation of dispatch reliability can be subjective, but good sources of information include:

- Vendors being considered for operation of the service. - Other aeromedical operations.

Helicopter and engine manufacturers. Other helicopter operators, such as

corporate, charter and offshore operators.

Operator Considerations There are approximately three dozen

vendors operating EMS helicopters. Choosing the right vendor is an extremely critical decision, and will be addressed at another time. Once selected, however, the vendor can offer helpful suggestions in selecting a helicopter. However-, two points should be kept in mind when reviewing these suggestions:

Make your landing approach safe wi th Tana Wire Maxkers

Can Y o u Afford N o t To?

For More Information Write or Call:

T A N A W I R E M A R K E R P. O. Box 370

California, Missouri 65018 (314) 796 - 3812

1. Previous experience operating a particular helicopter model should enable the vendor to provide a given service level more efficiently, and possibly more safely, than for a model with which the vendor is not familiar.

2. Some vendors may have a tendency to recommend helicopters which they already own/lease, if those helicopters are not being used elsewhere. In some cases these "idle capacity" helicopters are not the best choice for the aeromedical program.

Financial Considerations The financial considerations pertaining

to choosing a helicopter have not been addressed to this point. Generally, vendor lease rates will reflect operating costs and the acquisition costs of new helicopters. These acquisition costs start around $1 million for a multi-engine helicopter, and go up. Bear in mind, however, that you generally "get what you pay for." Increased safety margins from better single engine performance, larger cabin working areas, or IFR capability will all add to the cost.

Aeromedical programs should also consider financial alternatives other than simply contracting with a vendor to provide and operate the helicopter. The helicopter sales market is highly

cornpetitive, and manufacturer~ may offer some interesting purchase or lease packages. In some circumstances, purchasing a helicopter offers significant tax bcnefits, and can be accomplished wifia reduced financial risk when a working contract for that helicopter is assured. Relatively low contract prices oflcred by competing operators, however, ma? negate many of the financial benefits of Ibis option.

The process of selecting an aeromedical helicopter is complex, and no two programs have the same needs and requirements. A structured analysis is essential, and professional experience is important to ensure that all appropriate aspects are considered from an unbiased point of view. But once selected, the appropriate helicopter can produce benefits which far surpass the cost of its selection.

Noel G. Preston is Vice President of Aviation Consurting Incorporated. Based in Manhasset, New York, the firm specializes in corporate flight operations, and recently has participated in a number of program reviews and equipment selection projects nationwide.

Figure 1 HELICOPTER RANGE CAPABILITIES

(Ranges in Nautical Miles)

Payload 700 ibs 875 Ibs 1,050 Ibs 1,300 qbs

Hel icopter A 250 mls 195 mls 140 mls 80 mls Hel icopter B 345 290 - - - - Hel icopter C 335 335 335 335 Hel icopter D 265 265 - - - - Hel icopter E 250 250 250 250 Notes: 1. Payload must include medical personnel, medical equipment, and patient(s). 2. Assumes no-wind conditions. 3. Assumes helicopter will land with suitable fuel reserves remaining. Source: Aviation Consulting Incorporated analysis of manufacturer data.

Figure 2 HOVER OUT OF GROUND EFFECT

CEILING (HOGE) Typical Aeromedical Helicopters

Helicopter A Helicopter B Helicopter C Helicopter D Helicopter E

HOGE Ceiling (feet) Std.Day Std Day Temp.* Temp + 20 ° C.

4,9OO NA 7,700 4,600 6,400 2,000 5,300 2,800 8,200 5,000

*Standard day temperature equals 15 degrees C. at sea level. Source: Aviation Consulting Incorporated analysis of manufacturer data.

Figure 3 HELICOPTER CLIMB RATES

One Engine Inoperative

Helicopter Single Engine Climb Rate* Helicopter A 150 fttmin. Helicopter B 370 Helicopter C 740 Helicopter D 265 Helicopter E 690 *Assumes: Payload -- 700 pounds. Fuel for 200 nautical miles, plus reserves. One pilot. Altitude -- 3,000 feet. Airspeed above singre engine safe speed.

Source: Aviation Consulting Incorporated analysis of manufacturer data.

HOSPITAL AVIATION. JULY 1986 11