protocols have been exhausted. some air ambulance operations have full-time, on-site medical directors with pertinent backgrounds (e.g., emergency medicine); others have medical directors who are only available by pager. for those systems operating on the franco-german model, the physician is almost always physically present, and medical control is not an issue. equipment and interiors most aircraft used as air ambulances, with the exception of charter aircraft and some military aircraft, are equipped for advanced life support and have interiors that reflect this. the challenges in most air ambulance operations, particularly those involving helicopters, are the high ambient noise levels and limited amounts of working space, both of which create significant issues for the provision of ongoing care. while equipment tends to be high-level and very conveniently grouped, it may not be possible to perform some assessment procedures, such as chest auscultation, while in flight. in some types of aircraft, the aircraft's design means that the entire patient is not physically accessible in flight. additional issues occur with respect to pressurization of the aircraft. not all aircraft used as air ambulances in all jurisdictions have pressurized cabins and those that do typically tend to be pressurized to only 10,000 feet above sea level. these pressure changes require advanced knowledge by flight staff with respect to the specifics of aviation medicine, including changes in physiology and the behaviour of gases. there are a large variety of helicopter makes that are used for the civilian hems models. the commonly used types are the bell 206, 407, and 429, eurocopter as350, bk117, ec130, ec135, ec145, and the agusta westland 109, 169 & 139, md explorer and sikorsky s-76. fixed-wing aircraft varieties commonly include the learjet 35 and 36, learjet 31, king air 90, king air 200, pilatus pc-12 & pc-24, and piper cheyenne. due to the configuration of the medical crew and patient compartments, these aircraft are normally configured to only transport one patient but some can be configured to transport two patients if so needed. additionally, helicopters have stricter weather minimums that they can operate in and commonly do not fly at altitudes over 10,000 feet above sea level. challenges beginning in the 1990s, the number of air ambulance crashes in the united states, mostly involving helicopters, began to climb. by 2005, this number had reached a record high. crash rates from 2000 to 2005 more than doubled the previous five year's rates. to some extent, these numbers had been deemed acceptable, as it was understood that the very nature of air ambulance operations meant that, because a life was at stake, air ambulances would often operate on the very edge of their safety envelopes, going on missions in conditions where no other civilian pilot would fly. as a result, nearly fifty percent of all ems personnel deaths in the united states occur in air ambulance crashes. in 2006, the united states national transportation safety board (ntsb) concluded that many air ambulances crashes were avoidable, eventually leading to the improvement of government standards and camts accreditation. cost-effectiveness whilst some air ambulances do have effective methods of funding, in england, they remain almost entirely charity funded, as improved cost-benefit ratios are generally achieved with land-based attendance and transfers. health outcomes, for example from london's helicopter emergency medical service, remain uncertain. personnel the medical personnel of a helicopter ambulance has historically been a physician/nurse combination, paramedic/nurse, or a nurse/nurse combination. the need for a physician/nurse combination has diminished with more protocol and evidence-based applications for care by nurses and other clinicians and so the inclusion of respiratory therapists in all modes of air transport is becoming more prominent. retrieval doctor/physician retrieval doctor/physician: criteria for working as a medical doctor (known as "physician" in the usa) in aeromedical services depends on the jurisdiction. in australia, where aeromedical retrieval medicine is a well-established medical field, retrieval doctors must be experienced in a critical care specialty (i.e. anaesthesia, emergency medicine, intensive care medicine) as fully qualified specialists; specialty registrars in advanced stages of training; or general practitioners (i.e. family physicians) with broad experience in critical care and obstetrics. in the uk doctors working in hems are usually experienced in anaesthesia, emergency medicine, acute medicine or intensive care medicine. some general practitioners also work for air ambulances. a formal training programme for pre-hospital emergency medicine (phem) in the uk now aims to produce formal phem consultants who have underdone specific training in working in pre-hospital care and transfer medicine. flight paramedic flight paramedic: a licensed paramedic with additional training as a certified flight paramedic (fp-c) or a master's degree. the flight paramedic is usually highly trained with at least five years of autonomous clinical experience in high acuity environments of both pre-hospital emergency medicine and critical care transport. flight paramedics in the united states may be certified as a fp-c or a ccemt-p. flight nurse flight nurse: a nurse specialized in patient transport in the aviation environment. the flight nurse is a member of an aeromedical evacuation crew on helicopters and airplanes, providing in-flight management and care for all types of patients. other responsibilities may also include planning and preparing for aeromedical evacuation missions and preparing a patient care plan to facilitate patient care, comfort and safety. flight nurses may obtain certification in emergency nursing (cen), flight nursing (cfrn) or critical care (ccrn). civilian flight nurses civilian flight nurses may work for hospitals, federal, state, and local governments, private medical evacuation firms, fire departments or other agencies. they have training and medical direction that allows them to operate with a broader scope of practice and more autonomy than many other nurses. some states require that flight nurses must also have paramedic or emt certification to respond to pre-hospital scenes. hospital flight nurses the military flight nurse performs as a member of the aeromedical evacuation crew, and functions as the senior medical member of the aeromedical evacuation team on continental united states (conus), intra-theater and inter-theater flights - providing for in-flight management and nursing care for all types of patients. other responsibilities include planning and preparing for aeromedical evacuation missions and preparing a patient positioning plan to facilitate patient care, comfort and safety. flight nurses evaluate individual patient's in-flight needs and request appropriate medications, supplies and equipment, providing continuing nursing care from originating to destination facility. they act as liaison between medical and operational aircrews and support personnel in order to promote patient comfort and to expedite the mission, and also initiate emergency treatment for in-flight medical emergencies. transport respiratory practitioner main article: respiratory practitioner transport therapist: a highly trained respiratory practitioner (also called a respiratory therapist), typically utilized in long-distance transport situations, though able to provide care during shorter transfer. transport therapists may obtain adult critical care specialist (accs), neonatal transport specialist (npt) and neonatal pediatric specialist (nps) certifications from the national board for respiratory care. associations and organizations aerospace medical association: an umbrella group providing a forum for many different disciplines to come together and share their expertise for the benefit of all persons involved in air and space travel. association of air medical services: a non-profit 501c (6) trade association that represents and advocates on behalf of our membership to enhance their ability to deliver quality, safe, and effective medical care and medical transportation for every patient in-need. national or local organizations specializing in aeromedicine: british columbia ambulance service, airevac program royal flying doctor service (australia)