Helicopters & Planes
This article explains the differences between helicopters and planes, their advantages and limitations, as well as how to decide on the best option.
© UCL
In this article, Director of Nursing at New Zealand Air Ambulance Service, Angela Coward, discusses helicopters, planes and the special considerations planning aeromedical transfers involves.
There are two main methods of aeromedical transport: planes called “fixed wing” or helicopters referred to as “rotary wing”.
Working in aeromedical retrievals adds a whole extra layer to the work of the medical teams and it helps to understand how aviation operations are organised and regulated. Adding pilots, flight engineers and flight operators to the team requires good interdisciplinary communication and understanding. Patient and flight safety are equally important and only properly integrated medical and aviation teams will deliver the service safely to prevent incidents.
The balance of flight safety versus patient concerns has to be considered… if a flight has to be diverted due to poor visibility this will take priority even if it increases the transfer time and subsequent risk for the patient.
Key Points For Aeromedical Transfers
- Medical and aviation decisions to fly have to be separated
- Unsafe situations have to be identified, stopped and addressed immediately
- Strict adherence to aviation regulations is mandatory and trumps medical SOPs
Plane Or Helicopter?
The decision to use helicopters or planes depends very much on the set up of the service, the availability, distances to cover, financing and staffing as well as the patients needs. There is no “one fits all” solution. The range spans from primary missions or military retrievals to complex search and rescue missions and long distance secondary retrievals.
There is a huge variety of aircraft models and types. Some services use conventional airliners for transfer or deploy different types of ambulance jets. The use of ambulance jets or business jet charter allows retrieval of patients from almost any domestic airport compared to the use of airliners with dedicated routes and flight schedules.
Ambulance jet teams can accept patients which are otherwise not stable enough for airline transport, suffer from highly contagious diseases, or need special equipment (e.g. ECMO or an incubator). The drawbacks are significantly higher cost and sometimes refuelling stops, which add additional stress and risk to the patient.
The range of an aircraft is defined by the rate of fuel consumption and its ground speed.
There are also a number of technical factors that have to be considered by flight operators:
- Flight time and working time restrictions for the pilots and crew
- Speed of the aircraft
- Runway length required by the aircraft
- Distance covered without refuelling & planning of refuelling stops if needed
- Fuel and staff costs in relation to distance and stopovers
- Noise restrictions
The interior configuration, like with any vehicle, is also important for staff and patient safety and the ability to provide critical care. Have look at this picture in which a luxury jet has been transformed into a medevac flight. Can you spot any safety hazards?
As discussed earlier in this MOOC, all equipment must be fixed and accessible to prevent injuries, but in addition adequate lighting is needed for patient care but should not illuminate the flight deck, especially during night flights. Ideally the pilot should also be able to isolate themselves from the passenger cabin to avoid distraction or cross contamination.
Planning a mission is therefore very complex and the choice of the aircraft important. A turboprob plane costing USD 1000USD/hour might need five hours for a job, whereas a more expensive jet costing USD1500/hour only needs three hours for the same mission.
Different types of aircraft used by AMREF, Kenya, differing in range and cabin size
Limitations of transfers in an airliner:
Stretcher transport in economy class occupying 8 seats
Cabin Altitude
- Helicopters used in transfer medicine usually have no option to pressurise the cabin. However, it would be ideal for staff and passengers to maintain the sea level pressure of 101.3kPa (760mmHg) in the cabin.
- The equipment needed to maintain this pressure is heavy, requires a lot of energy and needs a reinforced cabin wall to withstand the large pressure differences between the cabin and the atmosphere.
- In fixed wing planes the cabin pressure is kept between 6000 and 8000ft regardless of the flying altitude. This is significantly lower than the cruising altitude but significantly higher than sea level. It is called cabin altitude.
- The Federal Aviation Administration (FAA) requires all fixed-wing flights to be pressurised at cabin altitudes of no more than 8,000ft at maximum operating altitude.
- Air inside the cabin is compressed and has very low water vapour content, making the circulating air very dry and cool. Due to the low humidity experienced onboard, the use of a heat and moisture exchanger or other means of additional sources of humidification are recommended.
Helicopters
- The mission profile of the service will define the type of helicopter used. Coast guard and SAR (Search And Rescue) services, for example, require aircraft with long range capabilities or good performance in altitude when operating in mountainous areas.
- HEMS helicopters will use helicopters with rapid start and response times, whereas dedicated inter-hospital transfer organisations will prefer models with large cabin capacities and a long range.
- Compared to fixed wing operations, vibrations in helicopters are much more noticeable and can influence the pulse oximeters and cardiac monitor measurements and cause nausea and vomiting in both staff and patients.
Secondary retrieval with the AAKSS HEMS team in the UK
Use of an EC135 for primary HEMS missions and urgent transfers. Example of “Christoph 28” stationed in Fulda, Germany
Most helicopter services operate under visual flight rules (VFR) conditions compared to instrument flight rules (IFR) conditions, which are used by commercial airlines. That means that the pilot needs minimum visibility. The VFR weather minimums are clearly defined for day or night operations, types of airspaces and altitudes.
Helicopter Landing Sites
Helicopter landing sites are dangerous places. The main risk is the impact with rotor blades or tail rotors and the significant down-wash when landing and departing. The strong wash can spray dust, sand, debris or snow and injure bystanders. The rotor blades dip lowest to the ground at slower speed when starting or shutting down the engines.
Transfer and retrievals are not necessarily covered by the legislation of HEMS operation and the use of certified landing sites is even more important. Hospital landing sites have to qualify and follow the aviation regulations with assigned approach and landing procedures. There are regional standards like the CAP 1264 (Standards for Helicopter Landing Areas at Hospitals) in the UK or the European Commission Regulation No 965/2012. The regulations define the requirements and options for heliports located at hospitals and the use at day and night time.
Example of a hospital helipad with correct marking, illumination, fire control, safety barriers and noise control.
Planning A Retrieval Flight
Part of the pre-flight briefing should be the discussion of the expected flight route, altitude and cabin pressure. It is possible for pilots to maintain sea level pressures by flying at low altitudes of about 15,000ft compared to the standard 30,000 – 40,000ft. However, this consumes much more fuel, is slower and the flight will be uncomfortable for staff and patients due to turbulence.
Questions to consider are:
- is the patient fit for air transfer?
- is a special set up needed for highly contagious diseases?
- how urgent is the transfer & is the staff qualified for this particular mission?
- are the weather and flying conditions suitable for the job?
- is a ground transfer to the aircraft necessary and feasible?
- is additional medical equipment required and will the aircraft tolerate the extra load?
- is a helicopter or plane the preferred option?
The choice of aircraft used for a transfer is therefore dependent on a balance of technical, logistical and clinical factors
© UCL
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