Safety Advisories

Helicopter Somatogravic Illusions



Somatogravic and Somatogyral illusions are the two most common forms of vestibular or ‘false sensation’ illusion which may be encountered when no clear horizon is present and flying wholly or partly by visual external reference is attempted.


The vestibular organs are part of the human body’s mechanism for achieving posture and stability. Changes in linear acceleration, angular acceleration and vertical acceleration (gravity) which occur as a result of flight control inputs, made to accomplish a change in the flight path, are detected by the vestibular system and may create either or both of these illusions.

Either illusion may arise in one of three ways

  • In the presence of an imperceptibly slow change in motion – in the case of roll at a rate of less than approximately 2° per second
  • After sustained – 10 to 20 seconds – acceleration in any one direction, it may be perceived that the acceleration has stopped.
  • When sensory stimulation from the angular motion of the head and of the aircraft occur simultaneously in two different planes – for example interrupting looking ahead to look up to an overhead panel whilst the aircraft is also in angular motion.

Both somatogravic and somatogyral illusions are most likely occur in conditions of marginal external visual reference or in visual ‘dark night’ conditions.


Whilst there are many situations in which these illusions can occur, one of the most likely, and certainly the most dangerous, is when the positive changes in acceleration, which accompany the initiation of a go around or the transition to initial climb after take off, are occurring. In both cases, the consequences can rapidly lead to CFIT if the condition is not recognised or to LOC if the situation is recognised but the complexities of recovery are mishandled.

Flap and gear retraction and changes in thrust whilst seeking to achieve and maintain a specific climbing flight path involve considerable changes in acceleration which, in turn, are conducive to a somatogravic illusion. As the inputs to establish sustained climb take effect, a perception of excessive pitch-up may occur. This can lead to a fear that the stalling angle of attack may be approaching. The instinctive reaction to this is to push the nose down in the belief that a reduction in pitch to a more “normal” climb angle is being achieved. If the aircraft is banked, either intentionally or unknowingly, at the same time, the perception of angular acceleration may be underestimated because of a somatogyral illusion, leading to an instinctive tendency to increase the angle of bank.

Sometimes, the strength of these illusions may be so intense that even a conscious cross reference to the flight instruments, which do not validate the perception, may be insufficient to lead to a corrective input to the flight controls by the affected individual. However, in a multi-crew aircraft, it is uncommon for both pilots to be similarly affected at the same time and effective monitoring becomes critical if the risk of an unintended excursion is to be avoided.

  • Be aware of this risk when operating in conditions where there is insufficient visual reference to assure safe flight entirely by reference to external visual cues.
  • Control the aircraft flight path by reference to the flight instruments whenever external visual cues are less than that required to fly by such external reference.
  • Anticipate the possibility of a pitch up illusion when acceleration occurs and a pitch down illusion when deceleration occurs. Remember than banking and angular acceleration increase the effects of any illusions.
  • At the first sign of any irrational flight control inputs by the other pilot, take control, especially if near the ground or where a sustained climb is essential for terrain safety.
Accident and Incident Examples
  • A320 Bahrain 2000: On 23 August 2000, a Gulf Air Airbus A320 flew at speed into the sea during an intended dark night go around at Bahrain and all 143 occupants were killed. It was subsequently concluded that, although a number of factors created the scenario in which the accident could occur, the most plausible explanation for both the descent and the failure to recover from it was the focus on the airspeed indication at the expense of the ADI and the effect of somatogravic illusion on the recently promoted Captain which went unchallenged by his low-experience First Officer.
  • A330 Tripoli 2010: On 12 May 2010, an Afriqiyah Airways Airbus A330 making a daylight go around from a non precision approach at Tripoli, which had been discontinued after visual reference was not obtained at MDA, did not sustain the initially established IMC climb and, following flight crew control inputs attributed to the effects of somatogravic illusion and poor CRM, descended rapidly into the ground with a high vertical and forward speed, The aircraft was destroyed by impact forces and the consequent fire and all but one of the 104 occupants were killed.
  • A310 vicinity Quebec 2008: On 5 March 2008, an Air Transat A310-300 was unintentionally mishandled by the flight crew during, and shortly after, departure from Quebec and effective control of the aircraft was temporarily lost. Whilst it was concluded that the origin of the initial difficulties in control were a result of confusion which began on the take off roll and led to a take off at excessive speed followed by subsequent mismanagement and overload, the inappropriate steep descent that followed was attributed to the effect of somatogravic illusion in respect of aircraft attitude control in conjunction with a singular focus on airspeed.

Precautions : Summer, Pre-Monsoon Flying

Summers and Pre-Monsoon Season are already here and with it the associated hazards for flying. Civil Aviation fleet is fortunate to have large percentage of highly professional, experienced and knowledgeable Civil and Ex-Military Pilots. However, it is essential to refresh the memory of the Operators, Pilots, Engineers, technicians and other associated personnel about the hazards associated with summer, Pre monsoon operations and the precautions which need to be taken to ensure safe and efficient conduct of operations.

Following Precautions Need To Be Observed During Summer, Pre Monsoon Months:-

  • Thorough Met Briefing, its professional interpretation and proper route planning becomes very essential during summer, Pre Monsoon months due to unexpected sudden changes in weather conditions.
  • Dust storms, thunderstorms, hail storms, Wind Shear are quite common during this period. Norwesters/ Kaal Baisakhi which affect areas around Chhota Nagpur Hills, Ranchi, Kalaikunda and Bhuvneshwar etc. are very dangerous for flying. Keeping yourself updated about the weather particularly thunderstorms, Norwesters   is very essential and monitoring these closely will go a long way in avoiding unfortunate accidents.
  • Lightening is a serious hazard during pre-monsoon months. Avoid thunderstorm areas particularly Norwesters. Confirm and ensure proper bonding of the Aircraft/ Helicopter.
  • Flying in Rajasthan and adjoining areas due to very high temperatures, severe turbulence and poor visibility over prolonged periods due to dust storms, is most demanding in summer months. Take due precautions.
  • Very widespread poor visibility conditions over a prolonged duration due to dust storms particularly in Northern India must be taken into consideration while planning flights. Diversionary airports/ helipads must be planned with due care.
  • Hailstorms during the summer, Pre Monsoon season are quite common and can cause serious damage to aircraft/helicopters while flying as well as when parked in the open. It should be ensured that weather radars are fully serviceable and pilots have adequate knowledge to intelligent use f weather radars for avoiding the hazardous areas.
  • Updrafts on the windward side of the hills and downdraft on the leeward side, valley winds  can pose serious hazards and pilots should factor this aspect while operating in hilly terrain.
  • Turbulent weather causing updrafts and down drafts can add to the fatigue factor to aircraft/helicopter, its crew and discomfort to passengers. Plan your flight altitude keeping these aspects in mind.
  • Bird activity in morning, evening hours and during day time at altitudes above 2000 ft (Birds also like cool higher altitudes during summer months) demands alertness on the part of pilots.
  • Proper parking and lashing of the aircraft/helicopters is much more essential during summer months since sudden occurrence of thunderstorms which are typical during this period, can catch you by surprise.
  • Fuel consumption increases during summer months and fuel planning should be done carefully.
  • Ensure that the aircraft/helicopter is properly bonded during refuelling operations. Lack of proper bonding has caused number of explosions of aircraft and helicopters all over the world.
  • Boiling of battery acids due to high temperatures, degradation of seals and other such material which may lead to leakage of oil/lubricants etc. should be kept in mind.
  • Adverse effect of high temperatures and dust during summer months requires parking of aircraft/helicopters inside hangars with proper covers.
  • Aircraft/Helicopter metal parts become very hot during summers and due precautions must be taken by aircrew as well as ground crew while working/operating the aircraft/helicopter. Use of proper gloves is recommended.
  • Frequent and close monitoring of the parameters of Engine, MGB, TGB and avionics equipment on board the aircraft/ helicopter is recommended since prevailing high temperatures may cause adverse effects. Degradation of electronic equipment is also quite likely during summer months.
  • Density altitude is considerably high during summer months. Power available from the engines also is degraded to certain extent due to high temperatures. Hence, the load carrying capability of the aircraft/ helicopter is reduced and should be given due consideration while planning the flight. Landing and Take-off distances increase considerably due to high density altitude obtained in summer months and should be factored during operations.
  • Ensure that there are no loose articles in the vicinity of the aircraft/helicopter which can fly and damage the aircraft/helicopter due to strong wind conditions experienced during thunderstorms.
  • Do not park aircraft/helicopter in the close vicinity of trees, poles, buildings and other obstructions which may get uprooted during storms and damage the aircraft/ helicopter.
  • Ensure that your aircraft/helicopter is not parked in areas which have dry grass fields in the vicinity since chances of fire to dry grass, vegetation are very high during summer months and strong winds may blow the fire towards the aircraft/helicopter.
  • Ensure that the helipads are sprayed with water to prevent dust from blowing due to down wash. Brief the concerned staffs to ensure water spray just 15 Mts to half an hour before take-off or landing of helicopter since the surface gets dried very fast and chances of dust being kicked up are very high.
  • Hot and humid climatic conditions add to the fatigue factor of the air as well as ground crew. This aspect must be kept in mind. Adequate rest and sleep in a cool comfortable place, commuting in AC vehicles, plenty of fluid intakes, moderate consumption of alcoholic beverages for those who like their chhota peg are some of the suggestion for consideration.
  • Always keep adequate supply of water and cold beverages on board the aircraft/helicopter to cater for unforeseen contingencies.
  • Ensure that the passengers are properly briefed with particular emphasis on turbulence and check the compliance of use of seat belts during flight.
  • Brief the ground liaison staff or concerned staff to make suitable arrangements for crew rest and recuperation particularly for operations from helipads.

Many Many Happy landings.


5 Vitally Important Safety Actions for Helicopter Pilots.

After analyzing dozens of helicopter accidents that resulted in fatalities for pilots and passengers, our team has uncovered five vital action items for pilots that will improve safe operations. Focusing pilots on these solutions will allow them to make better choices before and during their flights. The facts show that failure in these areas has resulted in lives being lost.

  1. Take Time for Your Walk Around – The pilot in command is responsible for determining the airworthiness of the aircraft he or she is operating.  An adequate pre-flight inspection and final walk around is key to determining the condition of an aircraft prior to flight. In addition, post-flight inspection can help to identify issues prior to the next flight. We believe that pilots would benefit from better guidance on how and why to conduct these inspections, as well as increased attention to their importance.
  2.  Communicate Risk Issues in the Cockpit – The flight environment is often dynamic and not every contingency can be anticipated or scripted in advance. The pilot in command is ultimately responsible for the safety of a flight, however, non-flying crew and passengers can and should work with the pilot to ensure safety. When unexpected changes are encountered, it is paramount that the pilot and crew members/passengers try to detect the elevation of risk, communicate it to each other, and collectively work through a reasonable resolution or mitigation. We believe that effective practices are needed for each stage in the process – detection, communication and decision.
  3. Get Solid Training for Make and Model Transitions – Transition training in the helicopter community is not uniformly applied, and this is leading to accidents because of unfamiliarity with airframe and/or equipment. We believe that documentation related to helicopter transition training can be developed into a new, unified guide that would offer recommended practices and a “toolkit” to support standardized use.
  4. Understand the Hazards of Over-the-Counter Medications – Because over-the-counter medications are readily available, pilots frequently underestimate the deleterious effects and the impairment caused by these sedating drugs. In spite of specific federal regulations and education efforts regarding flying while impaired, over-the-counter medication usage by pilots remains a factor in 10 to 13 percent of aircraft accidents. We believes that the helicopter community needs an increased awareness of the potentially disastrous results of operating an aircraft while taking these medications.
  5.  Make a Safe Attitude Your Overriding Priority – Safety in the aviation world can be defined in many ways. From the reactive point of view, safety essentially means a lack of accidents, an absence of injuries, and a general environment where things don’t go wrong. From the proactive point of view, this environment doesn’t exist for any consistent amount of time unless certain safety-related active principles are put in place and specific safety attitudes is fostered and strengthened. Whether we are strengthening a person’s safety attitude, bolstering a team’s safety convictions, or nurturing an entire safety culture, focusing every member of an aviation team at every level on clear and tangible convictions needs to be a central goal.

        Safety Aspects – Flying During Winters.

  • (a) Fog is a major flight safety hazard during winter months particularly in Northern, Eastern and to some extent in western India. Awareness about the phenomenon of fog is very essential for the pilots in particular. Pilots must be aware about the timings, extent, duration and severity of fog. Formation of fog and clearing of weather is very unpredictable. Although most of the time the met forecast is reasonably accurate yet there are many instances when pilots have got caught in very poor visibility conditions. Hence, it is very important for all operators to keep the hazards of winter flying in mind while planning flying.
  • (b) All the pilots should be current in instrument flying and should have undergone Ow Visibility Operations Training as per DGCA CAR.
  • (c) Thorough weather briefing must be obtained before undertaking any flying. Met office and internet are the sources which should be complemented with the experience of operating in particular area or region. Knowledge of typical weather phenomenon during winters will be of paramount importance.
  • (d) As far as possible, avoid flying during the early morning and late evening hours. Most of the times, the fog thickens at sunrise and may last for long hours before clearing or may not even clear for days.
  • e) Special precautions need to be taken while flying during night, dawn/ dusk. Night flying during winters should be undertaken with extra caution since poor visibility during night flying is a serious hazard.
  • (f) Low clouds which form as the fog is dissipating can be a serious hazard for flying during winter months and this aspect needs to be kept in mind. Low clouds may form very quickly and cover larger areas and particularly in the hilly regions, they can cover the entire valleys without any gaps for penetration.
  • (g) Fuel planning is of great importance since one may be forced to divert due to poor visibility conditions and most of the time, a diversion may not be easily available due to widespread fog.
  • (h) For Helicopters, It is always advisable to land at a suitable site if unable to proceed rather than persisting with the  hope  to find clear areas. This can be fatal at times.
  • (i) Ground contact flying should be the rule for helicopter pilots.
  • (j) Spatial disorientation is one of the serious challenge and hazard during poor vis conditions. Be familiar about it.
  • (k) Trust your instruments. In two pilot configurations, if the situation demands, then one pilot should be totally on instruments and other looking outside. Firmly resist the temptation of flying on instruments as well as looking out. This can be dangerous.
  • (l) Know the terrain and route safety altitudes well and plan your levels accordingly. Check, recheck and double check.
  • (m) Know the obstructions in your area of operations. Pylons, communication/chimney towers, electric/telephone cables, trolley cables particularly in hilly areas. All these obstructions pose a major hazard and knowledge of these is important specially for helicopter pilots.
  • (n) Trolley cables come up in hilly areas to cart apples from one hillock to other and vigilance is required to look for the same. Kindly intimate other operators in your area of operations about the existence of such hazards and mark them on maps.
  • (o) Operations in snow bound areas require special skill levels, Special briefing and training is essential for safe operations in these areas. Snow blindness (white out),blowing snow during pick up, hover and sit down, skids/wheels getting stuck in snow, slippery conditions while on snow or melting of snow during long hours of operations and disorientation(White out) are some of the aspects which need to be taken into account for snow bound area
  • (p) Ice formation at high altitudes is a serious hazard. Anti icing measures like serviceable and available ice detectors, heating elements, need for frequent movement of controls to prevent jamming of controls due ice formation, knowledge about freezing level and potential of ice formation are some of the areas requiring attention of the operators.
  • (q) For helicopters,before take off at high altitudes, ensure that the main, tail rotor blades and other surface areas are free of ice formation.
  • (r) Check the manufacturer’s instructions about adding anti –icing additives in the fuel and use proper additive as required.
  • (s) Check and ensure the serviceability of wind screen wipers,pitot heaters. Do not forget to switch on pitot heaters whenever required and switching them off on landing.
  • (t) Be aware that snow fall can change the appearance of the terrain and perspective during navigation and takeoff/landing.
  • (u) Batteries need to be maintained properly and protected during night from extreme cold temperatures by wrapping in blankets etc particularly for helicopters.
  • (v) Cracking of various seals can take place and must be checked periodically.
  • (w) Regular ground runs should be given at periodic intervals.
  • (x) Engineer and technicians should be told to ensure thoroughness during their maintenance and servicing activities. Tendency to take short cuts due to very cold temperatures should be highlighted and avoided.
  • (y) Low light conditions during winter months may result in minor cracks or other small defects getting overlooked. Ensure adequate lighting for servicing and maintenance work.
  • (z) Maintenance staff should be careful while climbing on the aircraft/ helicopter for maintenance work since surface may be slippery due to frost, icing etc.
  • (aa) Take special precautions during taxiing and maintain very good look out for obstructions, aircraft and vehicles.
  • (bb) Make sure that anti collision and nav lights are serviceable and switched on during flying.
  • (bb) Some time the slant visibility may be good but horizontal visibility may be bad. Be careful and aware.
  • (cc) Western disturbances may cause severe weather conditions during winters and hence be prepared to face them in safe manner.
  • (dd) Never take chances with the poor weather conditions and don’t be overconfident. Overconfidence has taken the lives of many pilots.
  • (ee) There may be occasions when frustration may set in because of the delays and postponement of departure timings/dates and long wait on ground due prolonged bad weather spells. Number of pilots have taken chances with weather under such conditions and have met with serious /fatal accidents. Please be aware of the grave danger under such conditions and take very considered decisions. Involvement of CEO’s, senior supervisors,op managers etc in close monitoring of operations can go a long way ensuring safety of operations.
  • Although efforts have been made to include as many hazards of winter flying as possible yet the list is not exhaustive. Operators may like to add other aspects which may be typical to their area of operations.
  • Operators should always endeavor to match the man with the machine, mission and weather conditions. Adequate instrument flying practice, simulator flying, currency, recency in area of operations, comprehensive briefing covering the entire spectrum of the various aspects of the operations and monitoring performance are key to the successful conduct of the operations. Respecting the weather and courage of conviction to say no if the safety of the flight is likely to be compromised must be impressed upon the pilots.



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