Delving into instrument meteorological conditions

Moody sky
IIMC: a medical team member's perspective

Proper knowledge of how to avoid IIMC and what medical crew and pilots should do when it’s encountered could help to prevent your crew from becoming a statistic. By Fred Ellinger, Jr., Joseph Schili and Randy Mains

You are the paramedic working as part of a rotorcraft EMS team including pilot and registered nurse. During your evening shift brief, the pilot-in-command (PIC) describes possible impending weather that may come ‘close’ to your company’s weather minimums, but feels the weather should remain ‘flyable’ throughout your 12-hour shift.
At 01:30 hours, you are alerted for a flight approximately 35 miles (55 km) from your base. As you prepare for the flight, the pilot advises he has checked weather at your airport and along your route. He reports the ceiling and visibility are lower than expected, but should be ‘OK’ for the mission. The pilot tells the communications centre: “We’ll take a look”. On departure, you notice the beautiful halos around the blue and orange airport lights.
Approximately 15 miles from your intended destination, you begin to notice the illusion of the horizon becoming less visible. The halos you saw at the airport earlier are now visible on every light you see, but now appear larger and denser. You raise your concerns to the pilot, and he assures you he will be able to make it to the scene. You notice the pilot begins leaning slightly forward in his seat and appears to be concentrating on the outside as the aircraft begins slowing and losing altitude. The clouds appear to be much closer to the blades of the aircraft now, and it seems you are traveling lower and slower than a moment before. You become increasingly nervous. Moments pass, now you can see nothing in front of the windscreen as if someone has turned up the cockpit lighting and you can no longer make out any visual references in front of you or on the ground. You have now lost all visual cues in space and cannot tell if you are level, banking, turning, or even upside down. You begin to panic. You have gone into inadvertent instrument meteorological conditions (‘inadvertent IMC’ or IIMC) – a killer of many flight crews in the US and around the globe. Failure of the pilot to properly recover is almost a certain death sentence for you and the team.

IMC flight is one of the most demanding, disorienting, and dangerous conditions a pilot can experience

IIMC defined

The US Federal Aviation Administration (FAA) states instrument meteorological conditions (IMC) exist during times of rain, low clouds, or reduced visibility, with the legal definition being: whenever visibility falls below three statute miles, the ceiling drops below 1,000 ft above ground level (AGL) or there is no visible horizon. Routine IMC flight is governed by instrument flight rules (IFR). IFR flight is provided under positive control of air traffic control (ATC). IFR flight requires specific aircraft equipment, added pilot qualifications and pilot proficiency standards. For these reasons, most rotorcraft EMS programmes are not IFR capable.
IIMC exists where deteriorating weather conditions prevent flying visually under visual meteorological conditions (VMC).

IMC flight is one of the most demanding, disorienting, and dangerous conditions a pilot can experience1. These encounters result in the highest percentage of fatal injuries from helicopter accidents. Figures (not EMS specific) from US National Transportation Safety Board (NTSB) research in 2011 show that 45 of the 52 IIMC accidents occurring that year were fatal. That equates to a 13-per-cent survivability rate if you suffer an accident after going IIMC!

Artificial horizon

A review of rotorcraft crashes

In 1988, the NTSB concluded that poor weather poses the greatest single hazard to EMS helicopter operations2. The risk weather poses to the successful outcome of any air medical mission is unquestionable. Despite advances in weather reporting and forecasting, training, education, technology and crewmember resource management (CRM)/air-medical resource management (AMRM), weather remains an all too constant factor regarding crashes. Despite the common knowledge that poor or deteriorating weather can exponentially increase the risk of an accident or incident occurring, we constantly read about our colleagues dying or being severely injured while flying in conditions that leave us asking, “What were they even doing out there in the first place?” Interestingly enough, it often does not appear to be a pilot’s disregard for weather minimums when accepting a mission – rather, it is the in-flight encounter with deteriorating conditions while en route that initiated the fatal chain of events2.
Of note, a NASA-AMES Research Center report found that pre-flight weather briefings were obtained in 80 per cent of the missions studied, but in 75 per cent of the briefings provided, the weather given did not match the actual conditions that were encountered in-flight3.
In the 1980s, approximately 22 per cent of helicopter EMS crashes were noted to be weather-related2. In the 1990s, this figure grew to approximately 32 per cent. Although the total number of crashes during this time had decreased, the number of weather-related crashes grew by 10 per cent2.
Weather-related crashes also tend to be more severe in nature, with approximately 75 per cent of the crashes resulting in at least one fatality, and more than two-thirds having no survivors at all2. Another factor regarding weather-related crashes is the fact that 88 per cent of weather-related rotorcraft crashes occurred at night. Interestingly enough, these weren’t during take-off or approach and landing operations, but rather during cruise flight with inadvertent entry into meteorological flight conditions being the culprit2.
At the 2010 Air Medical Transport Conference in the US, Sandra Hart of NASA-Ames Research Center presented a study which concluded that nearly five times as many EMS rotorcraft accidents occurred during IMC flight, with nearly all of them involving IIMC4.

The IIMC experience

As previously mentioned, flight into IIMC, particularly for the inexperienced team member, may be extremely frightening and overwhelming. Psychologically, you may experience feelings of helplessness, fear, loss of control, and outright panic. Physically, you may experience spatial disorientation, a loss of relationship of one’s body orientation and/or position within space, creating vestibular as well as other illusions that ‘trick’ your brain into not knowing where it is. If you are not aware of these conditions, spatial disorientation may occur without your knowing it. Spatial disorientation kills, because without visual cues, you cannot trust your other senses to keep you properly oriented. In general aviation, spatial disorientation occurs in five to 10 per cent of all accidents, of which 90 per cent are fatal5. The FAA has published a short safety brochure on spatial disorientation, recommended reading available at:
In IIMC conditions, it is important that you don’t panic! A panicked team member is useless to the pilot and creates a distraction. To avoid panic, it is important that you take steps to avoid spatial disorientation. Unfortunately, other than avoiding flights that could result in IIMC, the only way to combat spatial disorientation is to rely on the aircraft’s flight instruments. For the pilot who is properly trained and practised, this should be second nature. However, many seasoned pilots fail to be able to immediately go from flying visually to transitioning onto the instruments. For the medical team member, this training is something you must usually seek out and learn on your own as many operators do not provide any such training. To avoid spatial disorientation, the artificial horizon, also called the attitude indicator (Figure 1),Figure 1 is your primary instrument, as it shows the aircraft’s rotation about both the longitudinal and vertical axis (left or right), and lateral axis (nose up, level or down). Focusing on this instrument will provide you with visual confirmation of your position in space relative to the horizon. Despite what you are feeling through your inner ear and the ‘seat of your pants’, one must learn to disregard those feelings and put total trust in the instrument! When viewing the attitude indicator, remember ‘brown is ground’ and ‘blue is sky’, meaning that if the aircraft is correctly oriented, blue will be above brown. If both team members are in the patient compartment and cannot see the attitude indicator, a length of medical tape can be hung from the ceiling and the roll end to hang freely. This will give team members a visual reference to the relative attitude of the aircraft.

IIMC checklist

Preventing IIMC

Despite education, training, experience and ratings, it still remains possible for any pilot to encounter IMC while in flight, even in the absence of poor or deteriorating weather. Night missions, for example, with no illumination or over terrain with no visible horizon can lead to IIMC and pose the same risk. Even an instrument-rated and current pilot may not trust his or her instruments and fall victim to spatial disorientation, accelerating the chain of events toward a fatal outcome. That is because they may be instrument rated, they may have satisfied the regulations for being instrument current, but they may not be instrument proficient. Flying by reference to the flight instruments is the most perishable skill a pilot has. If not practised frequently, that skill is easily lost.

You can take the following steps to reduce your chances of encountering IIMC:

Flying by reference to the flight instruments is the most perishable skill a pilot has. If not practised frequently, that skill is easily lost

  • Thorough shift briefings to include detailed current weather conditions, forecasted weather conditions and known or suspected micro weather patterns.
  • Pay special attention to light or no wind conditions with a temperature and dew point spread of 3° or less. This is indicative of possible fog or low-lying cloud formation.

Obtain personal knowledge of weather in your flying area. Make it your job to understand the details of a basic weather report.

  • If weather is of a concern, personally check multiple automated weather observation stations (AWOS) where you are located and around your service area. Monitor them for deteriorating conditions.
  • A complete listing of surface weather observation stations can be found here:

Hold a prelaunch weather briefing to include local and enroute forecasts including AWOS, METAR (routine aviation weather report issued at half hour or hourly intervals), and terminal area forecasts (TAF) when possible.

  • If in doubt, call or look for yourself. A good tool to use is the NOAA/National Weather Service’s Helicopter Emergency Medical Services Tool found here:

Here are some visual cues that weather may be deteriorating:

  • Halos around lights.
  • Precipitation. Visibility can become limited in and around rain or snow showers/storms. Ceilings can also fall during precipitation events.
  • Fog or cloud layers including marine fog.
  • Building ground-level fog.

Avoid flight in marginal weather. Remember the saying, ‘three to go, one to say no’. Trust your gut. If you are not comfortable, you not only have the right but the responsibility to speak up! No reputable programme will argue with your decision. Make your concern known in no uncertain terms. Be stern advocating your position if need be.
Use the US National EMS Pilot’s Association (NEMPSA) Enroute Decision Making Point (EDP) tool to either turn around, land or go IFR if able, but you do not continue6. How the EDP works:

  • If you decrease your airspeed 30 knots less than cruising speed, you’ve reached that point.
  • If you descend to 300 ft below your minimum enroute altitude during the day or 500 ft at night, you’ve also reached EDP.
  • In either case, you now turn around (if safe to do so), land, go IFR if able, but you do not continue. Use of this tool is recommended as any team member can identify its criteria and recommend immediate action before IIMC is encountered, thus keeping the team safe.

Expect proper IIMC procedures to be followed

Knowing proper IIMC procedures is important. Like instrument orientation, not many programmes offer much information on proper flight procedures, particularly those for IIMC. These procedures are often thought to be only the pilot’s responsibility. We disagree. The team, although lead by the pilot, is in fact a team. All team members should know emergency procedures, including IIMC. Failing to know how your pilot should react in a situation places your life and the lives of others onboard the aircraft at risk. IIMC is an emergency and should be treated as such. If you encounter IIMC and the pilot does not react accordingly, it is incumbent upon the medical team member(s) to request he or she do so. The time to react may be very limited and immediate action on the part of the pilot is required.
According to an FAA study: “Tests conducted with qualified instrument pilots indicated that it can take as long as 35 seconds to establish full control via instruments once visual reference to the horizon is lost.”7
As with any in-flight emergency, the first action taken should be implementation of the ‘sterile cockpit rule’. That is, everyone limits conversation to only safety-of-flight issues. The next actions that should be taken revolve around the safe recovery of the aircraft. The immediate action steps which should be expected can be referred to as the ‘4 Cs of IIMC’. They are:

  • Control – If necessary, remind the pilot to abandon his exterior scan and focus on flying the aircraft relying on their primary instruments. The pilot should engage the autopilot immediately if available.
  • Climb – “Once you encounter IIMC the ground is no longer your friend.” Once under control, the pilot should climb the aircraft straight ahead to a safe altitude. If necessary, based on your assessment of radar altimeter or pressure altimeter, clearly state, ‘Climb!’. As a medical team member, no one expects you to know how to read aviation charts or know maximum elevation features. However, it is important that you have a general idea of the minimum safe altitude for the area where you are flying.
  • Course – After positive control of the aircraft is obtained and you are at a safe altitude, a course deviation may be made. The pilot may initiate a turn to avoid known obstacles or divert to a location with better weather conditions or to an airport where an instrument approach can be made.
  • Communicate – After positive control of the aircraft is obtained, a climb has been initiated and the aircraft is on course, the pilot should contact air traffic control. An emergency should be declared and intentions/assistance needed should be relayed to the controller. Unfortunately, in many cases this procedure is not followed with disastrous results. ATC can provide lifesaving co-ordination with the pilot and aid in safe passage to a location with known good weather or give him/her radar vectors for an instrument approach.


Flying the aircraft is the legal responsibility of the pilot. However, safe operation is the responsibility of every team member. The following crew resource management functions may assist the pilot and ultimately the safety of the flight.

  • Identification of missing emergency IIMC recovery steps. Using a checklist, a team member, no matter where seated, can ‘back up’ the pilot’s actions. (Figure 2/Figure 3)Figure 3 Keep the pilot situationally aware of deteriorating conditions. An example would be telling the pilot, “I can’t see the horizon or ground any longer. Come inside and look at your altitude or attitude.”
  • If the pilot is task-saturated or the aircraft does not have an autopilot to help them, the pilot may need you to make radio calls for them. You may be asked to select frequencies and contact ATC to declare an emergency and request assistance. Calls on company frequency are least important and should be the last to be made.
  • Assist in obtaining needed radio frequencies from either the GPS, appropriate sectional chart or IFR plate.
  • Assist in setting GPS as requested.
  • Access the appropriate IFR plate and provide the pilot with requested information.
  • Perform other duties as requested.


IIMC is an unnerving and potentially deadly situation, even for an experienced pilot and flight team, and should be considered a true emergency. It is important for all team members to understand IIMC, its avoidance and recovery techniques. Although many operators omit medical team members from formal IIMC/IFR training/procedures, it is important for the medical team members to seek out this information on their own to increase their personal knowledge. During an emergency, including IIMC, anyone’s experience and knowledge can aid in the successful resolution of the situation.
In an effort to eliminate rotorcraft EMS crashes as a result of IIMC, it is paramount you speak to your pilots and operators about proper IIMC avoidance and recovery procedures. Good CRM and AMRM requires that you speak up when you have a concern – don’t ‘suffer’ in silence thinking the pilot or the other members of your team have the same awareness as you do. Don’t let intimidation or fear of retaliation for cancelling a flight for weather influence your decision making. Your safety is paramount. Trust your gut. Remember: three to go, one to say no!