BASICS OF AN AERODYNAMIC STALL

This is written from a pilot’s point of view with the aim of giving a theoretical aerodynamic background to the actions that one takes in the cockpit. These actions would become instinctive if one understands the basic theory. We are not designers or engineers, but we need to fly the aircraft safely from A to B, under all conditions. Under normal conditions we would never be operating close to stall. The highest AsOA that we encounter in flight are during the take-off and landing phases.  However, when operating under conditions that are not normal we are still required to fly that aircraft safely and thus we need to understand how our aircraft behaves at all times.

• ·         In flight we have four forces that we should be aware of at all times. To maintain steady straight and level flight the Lift has to balance weight and the thrust has to balance the drag, and the sum of the moments has to be zero. This also implies that the Power available is equal to the power required. If the Power available is more than the Power required then the aircraft would have a ROC, and vice versa. Power required = Drag X TAS. Power available is Thrust X TAS.
• ·         A stall is a condition of flight in which the aircraft has exceeded the stalling angle of attack or the critical angle leading to a sharp decrease in co-efficient of lift and a sharp increase in the co-efficient of drag. (Please refer to the AOA vs Cl/ Cd graphs).
• ·         The decrease in Cl leads to loss of lift as L = Cl ½ pv2S. In straight and level flight the lift is now no longer able to balance the weight.
• ·         The increase in co-efficient of drag increases the drag leading to a power deficit, as the power available at the same throttle settings is now less than the power required. On a training aircraft with rectangular wings, propeller slipstream and high thrust line, the wing stalls and the nose pitches down, helping in recovery of the aircraft from the stalled condition.
• ·         This situation changes in aircraft that fly at high altitude, high speed, have sweep back wings and a thrust line below the CG (due to low slung engines). Sweep back wings tend to stall at the tips first causing the nose to pitch up; any addition of thrust from the low slung engines would aggravate the pitch up situation and lead to a stall.
• ·         In a power deficit situation, the aircraft will develop a descent. When the aircraft commences descent, the direction of the relative airflow changes, as the flight path of the aircraft has changed.  The relative airflow comes from further below than earlier leading to an increase in AOA – reducing Cl further and increasing Cd further. We are now entering into a deep stall zone which is more pronounced on sweep back and delta wings. The positioning of the tail also has an effect.  Any other phenomenon like icing could also lead to reduction of Cl and increase in Cd.
• ·         The only way out is to unstall the aircraft by reducing the AOA by aligning the aircraft with the relative airflow coming from below OR in pilot’s parlance by pushing forward on the control column. The throttle is advanced to increase the thrust so that the power available increases to match the power required.
• ·         Once the aircraft unstalls, the aircraft can be eased out. This procedure has to be followed on all aeroplanes – the basic theoretical considerations do not change very much and you can understand the reason why ; the manufacturers give the finer points which would be peculiar to that aircraft type.
• ·         The basic fact is that whether one flies the C-152 or the A-380, the aircraft needs to be supported by the air in which it flies.
• ·         The airflow going around the aerofoil is what generates the lift and the aerofoil (and in turn the wing too) stalls when the airflow ‘separates’ from the aerofoil at a forward position on the chord, leading to sharp loss of lift. (As the AOA increases, the separation point keeps moving forward.)
• ·         Every aerofoil has different aerodynamic characteristics, as can be seen in the books. When icing takes place the aerofoil shape changes, and so do its aerodynamic characteristics – Cl, Cd and separation of airflow too. It would happen every time the aerofoil shape changes – it could be because of dirt, pigeon shit on the wing or any other phenomenon.
• ·         Standard operating Procedures are laid down for all normal operations that a company undertakes, and are a pilot’s life line and should be followed meticulously to go from A to B safely under all conditions – normal or not normal.

An Aircraft Incident - Good CRM

On 25 Oct 2005, Capt. L Marcelo (Brazilian pilot with 8400 hours) and F/O Thomas Abraham (Indian with 939 hours) were scheduled to operate flight BD 201 from Kolkata to Chennai. The crew arrived at flight operations about 0:50 mts before scheduled departure. After a detailed briefing by the FDO, the crew proceeded to the aircraft and spoke with the engineer at the aircraft regarding the snags reported by the previous crew. F/O Abraham was the PF for the first sector from Kolkata to Delhi. There was a slight delay on the part of ground operations and this time was utilized by the crew to discuss various operational aspects connected with the flight. Departure was from R/W 01R. During the take off roll, all callouts were made by Capt. Marcelo. All parameters were normal during the ground roll. After unstick, on selecting gear up, at around 400’ agl a loud bang was heard. This was followed by a yaw to the right, and high vibrations. Capt Marcelo took over control of the aircraft, made a quick scan of the engine parameters and found that there was a rapid rise in the No. 2 engine EGT, which was going beyond limits. Capt Marcelo partially retarded the No. 2 engine thrust lever in order to contain the EGT, while at the same time climbed to the security altitude of 800’. F/O Abraham made a PAN call to the ATC. At security altitude, Capt Marcelo asked for MCT on live engine, engine failure shutdown checklist and after take off checklist, in this order. Both crew members concurred that the No 2 engine was malfunctioning, and the checklist was called out by F/O Abraham. The flaps were left at flap 1 position, as the crew operating the previous flight on this aircraft had reported difficulty/ vibration while deploying flaps. Also, the Capt was not sure if the flap assembly had sustained any damage during this emergency. Capt Marcelo had the field in sight and elected to do a visual circuit to minimise the time in air. On D/W, the one engine inoperative descent approach checklist was carried out by F/O Abraham, followed by the one engine inop landing checklist. An overweight, flap 15 landing was carried out at a Vref of 150 kts. The landing was normal with manual braking, and No. 1 engine reverser deployed. Taxi in and shutdown was as per SOP. The tyres of the right main landing gear deflated on reaching the bay. The cause of the incident has been attributed to internal object damage caused due to fatigue failure of 3 blades of the HP Turbine. The engine sustained extensive damage to the HP and LP turbine section and downstream of the turbine.

Capt Marcelo and F/O Abraham had arrived in Kolkata on 23 Oct 2005 after operating BD 102 from Chennai to Kolkata. This was their first flight together as a crew. The crew utilized the extended stay in the hotel at Kolkata to get acquainted with each other, personally and professionally. During this process, one of the situations put forward by Capt Marcelo was a condition of an engine failure after take off. They discussed the actions in such a situation and agreed that priority should be given to flight path control, followed by the appropriate checklists and a landing back at Kolkata. Overweight landing was discussed, and Capt. Marcelo opined that single aisle aircraft undercarriages were designed to perform overweight landings as the difference in their MTOW and MLW was not very large. Also, that it was preferable to carry out an overweight landing in such a case, as the cause of engine failure would not be known to the crew, and thus such an eventuality should be treated with the same priority as an engine fire.

Crew Resource Management highlights

1. There was a large difference in the flying experience of the crew. In addition to this, there were cultural differences too considering the nationalities of the crew. This was also the crew’s first time together. Capt. Marcelo understood the importance of CRM and thus took advantage of the time available during the extended stay at Kolkata to get to know F/O Abraham better, both personally and professionally.
2. During this interaction, situational emergencies were discussed, including an emergency of engine failure after take-off at Kolkata.
3. The Captain immediately took over controls on encountering the emergency, with the F/O taking over the duties of PNF (PM). The F/O alerted the ATC with a PAN call, and carried out checklists as per the directions of the Captain.
4. The previous discussion of a similar situation helped the decision making process in this case, in terms of overweight landing and the other actions pertaining to the emergency situation.
5. Open cockpit communications helped optimize performance of both crew members.
6. Both crew members concurred on the engine malfunction before taking action.

CREW RESOURCE MANAGEMENT (CRM) AND THE AIRCRAFT COMMANDER

Formal CRM training started sometime in the 70s; the first being KLM that introduced a human factors training programme, based on the Edwards SHEL model and the trans-cockpit authority gradient. Accidents involving fully airworthy aircraft were perplexing the aviation community – the most notable example being the collision of two B-747s in 1977, while on the runway at Tenerife. Accidents like these were pointing towards the breakdown of crew co-ordination and communications between the cockpit crew. It was finally the NASA workshop of 1979 where the role of human factors in aviation accidents came in to sharp focus. Participants at this conference were convinced that formal training in crew co-ordination was required to reduce accidents due to human error. The origin of CRM (initially called Cockpit Resource Management and later changed to Crew Resource Management in recognition of the complex nature of aviation operations - where human errors, anywhere in the chain, can lay dormant for extended periods until an active failure at the hands of pilot leads to an accident) training is now universally traced to this NASA workshop of 1979. As more knowledge was gained on the subject the training has undergone many generational changes, from the first generation CRM to the present day sixth generation CRM, also called Threat and Error Management. CRM training is crucial for flight crew (besides for others too who are connected with aviation) as they are aviation’s last of line of defence to prevent an accident from happening.

 Amongst the flight crew, the Commander of the aircraft has been given the final authority with regards to the safety of the aircraft, and its contents, from the time he/ she assumes command until he/ she relinquishes the command of the flight. This is elaborated in Rule 141 of the Aircraft Rules, which states that “The Pilot-in-command (PIC) shall have final authority as to the disposition of the aircraft while he is in command.” The rule also states that the PIC “shall supervise and direct the other members of the crew in the proper discharge of their duties in the flight operations.” It further clarifies that “In addition to being responsible for the operation and safety of the aircraft during flight time, the Pilot-in-command shall be responsible for the safety of the passengers and cargo carried and for the maintenance of flight discipline and safety of the members of the crew.” This is indeed a very onerous task for any one individual, especially one who is flying above mother earth, in the third dimension. Why?

It is because the PIC is human, and has all the capabilities and limitations like any other human being. These capabilities and limitations have been studied by experts in the respective fields. These are required to be known by pilots to get any aviation licence, and pilots are also being tested for the same, before issue of the licence. ‘Human factors’ is the term designated by the ICAO for this important area of study by pilots (and lately by others like ATCOs, Maintenance too). This article is not going to go into details of the physiological factors like hypoxia, hyperventilation, decompression sickness, fatigue, sleep, etc. or the factors like illusions that most of the pilots are familiar with. The author has participated/ facilitated CRM training and always felt that the training mainly focussed on the ‘What’ and ‘How’ of CRM, after briefly telling the participants about ‘Why’ it is important for the aviation industry to have an even lower accident rate. It is the author’s view that if the CRM training focussed more on convincing the participants of the ‘Why’ it is important for the participants, then the person would be more receptive, and self motivated to listen to the ‘how’ and ‘what’.

This article will attempt to make a strong case for ‘Why’ CRM is important for any crew, and especially so for the Commander because it is the Commander who finally signs on to the task of undertaking a safe flight from A to B, with the help of the crew, of course. It seems simple and every Commander intellectually understands its importance, but this fact needs to be internalised and acted upon if we want to prevent accidents like the one at Mangalore, and others around the world, where in fully serviceable aircraft met with fatal accidents.

 It is a fact that with the new generation of highly reliable aircraft and engines, the major cause of accident is due to factors that are termed as human error. When an accident does[J1]  take place due to human error, it was found that the accident happened due to the active failure in the hands of the pilot, but a number of passive errors had happened at various stages in the life cycle of the aircraft viz., the design, manufacturing, loading, servicing stage, etc. or have been caused due to an error by the regulator, company management, ATC, dispatch or by the meteorologist. The other fact is that in some cases the PIC was the final person who could have prevented the accident from happening. A human error accident in the hands of the pilot is an acceptance by industry professionals that the accident could have been prevented; thus a human error (aircrew) is more appropriately a ‘pilot preventable’ accident. This brings us to larger questions – Firstly, Do human beings like to err? And the answer is ‘No’. Secondly, do humans err?  The answer is ‘Yes’. Think of the number of times one tries to open the lock with the wrong key, or punches in the wrong password. This implies that although no human likes to err, ‘to err is human’. This also implies that PICs, being human, are also prone to errors. Why?

Research in to the human brain has brought out a large number of limitations of the brain. The following are some of the important memory (storage and retrieval of information) problems that most human beings, including pilots, suffer from: -

• Absent mindedness – Forgetting due to lack of attention.
• Blocking – Temporarily forgetting – “did he clear us to land?”
• Transience – Forgetting information with time – “What is the Approach frequency…?
• Misattribution – Forgetting the source of the information.
• Suggestibility – Developing a false memory because of new information received during retrieval.
• Bias – Unconscious reshaping of memory due to personal beliefs or mood.
• Persistence – Negative distortion of a memory of a traumatic event.
• Memory changes – Memory changes from person to person, and also within the same person due to reasons like physical & emotional health, stress, quality and quantity of sleep, diet and age.
• Inattention blindness - Attention resources are very limited and it is a known fact that things to which we are not paying attention to are not perceived; more importantly if we are devoting attention to one task, then we may not have adequate attention resources for other maybe more important primary tasks – fixation – a cause factor in many aviation accidents. Inattention blindness is affected by the following  factors:
• Conspicuity – All warnings in the cockpit are designed keeping this in mind.
• Mental workload and task interference
• Low workload and the effects of automation – Low arousal; low performance.
• Limited processing capability of the brain as compared to large acquiring capability of the five senses. In aviation eyes, ears (hearing and vestibular apparatus) and seat of the pants are the most relevant sense organs. For example in the human visual system, the amount of information coming down the optic nerve is estimated to be in the range of 10 million bits per second. This far exceeds what the brain is capable of fully processing and assimilating; about 16 bits/ second (max 40 bits/ second). Guess why two people looking at the same scene would pick up different images – this is primarily based on what is being paid attention to by each of them.
• Limitations (in terms of time, and capacity) of the working memory (like the RAM in the computer) in humans.

These severe limitations of the human information processing mechanism would convince any human about what he is up to when he/ she is interacting with the outside world and trying to make sense of what is going on, or in aviation parlance when he is trying to get and remain situationally aware.

This already difficult situation becomes even worse when the same set of information is to be processed under time constraints, like in a non-normal or unanticipated situation in the air. Being situationally aware at all times is very important for a crew primarily because without being situationally aware it would not be possible to take the right decisions every time. Poor situational awareness leads to bad decisions; a situation that is detrimental to the task at hand – of ‘flying the aircraft safely and efficiently from one place to another’ – the primary task of the PIC. How do we ensure that we are situationally aware at all times, or regain situational awareness at the earliest, if it is lost due to any reason?

This requires the application of crew resource management – “the effective use of all available resources: human resources, hardware, and information.” The PIC is the final decision maker in the air, but knowing his/ her limitations, he should be the one who makes all efforts to use all available resources to become situationally aware, and there after go on to making the right decision. This sounds simple and logical but a glance through the history of aviation accidents/ incidents would be able to convince any pilot that this is not so. The reasons are many. The reasons could be attributed to the way in which an average human grows up in this world – our formative years in school where we are taught to excel as individuals and compete with each other to stand first in class/ sports etc. The same pattern continues through college, and life there after – our individual successes are celebrated. When we enter aviation, our first solo is the most celebrated event, and solo flights are cherished by ‘real pilots’. ‘The individual is required to be competitive, and is complete’, is the message that life has given us thus far. Even our traditional checks and proficiency testing in aviation are done on an individual basis – testing is of our skills as individual pilot’s (a column for CRM has also been added to the check proforma to assess the pilot’s CRM behaviour). The early pilot’s with the leather jackets, white silk scarves and glasses is the macho image of a pilot, which even today is ingrained in many individual pilot’s minds, some of whom have never been close to a fighter. The author flew single seat fighter aircraft for over two decades and can vouch for the fact that he always felt complete – missed out a few checks here and there; made approaches on the wrong runway; had ‘action total’ on first solo; miscalculated fuel in the air while doing low level navigation, etc. Single seat fighter flying accepted a certain amount of risk due to the nature of the task, but commercial aviation is required to be safe, and risk free. Commercial pilots have to work with a different mindset where the aim safe and efficient flying has to be kept paramount.

Commercial pilot’s need to be convinced about using CRM techniques, if we wish to better aviation’s accident record. The rapid growth in aviation, leading to a larger number of departures, in the coming years would lead to larger number of accidents, if nothing is done to bring down the accident rate/ million departures. The accident rate in commercial aviation has been brought down substantially over the years, from the 1950 – 60s, due to the move from  reciprocating engines to the more reliable jet engines as a means of propulsion,  and due to usage of better technology. However, the accident rate has stagnated at a low figure over the past few decades – it has refused to reduce any further. The major cause of accidents is now human factors. Aviation’s greatest challenge is to tackle this cause factor if we wish to reduce the number of accidents, with the growth of aviation. The most significant contributions to reducing human error accidents can come from internalisation of CRM techniques by the pilot community, because the pilot is the last line of defence of preventing accidents in the aviation system.

Being situationally aware in terms of our location, spatial orientation, environment, aircraft systems, time and fuel requires all inputs that are available to the PIC. It has been found in many accidents that the accident happened in the hands of a situationally unaware PIC, when he was the PF, even though other crew members were situationally aware – the Mangalore accident is our own case in point. What this implies is that the whole crew should be on the same page and there should be no unresolved issues in the cockpit. It is not the PF who causes an accident; it is the entire crew. Accidents happen because either the PIC does not ask for, or permit (through verbal or non verbal communications) free flow of relevant information between the crew, or the crew does not share the relevant information due to reasons that are part of being human. You can be disrespectful/ rude to a machine and it would even then give you the right information if you have pressed the right buttons and controls, but humans are different – we are emotional beings. Emotions are facts as far as humans are concerned. Our life should convince us that emotions always matter. Other reasons could be: a human may feel that the other is aware; knows every-thing; or the other does not need to be told as he is so experienced; or a plain ‘I am not OK, you are OK situation’; or ‘why should I tell him’ he is responsible for his actions. These may be false assumptions, as has been brought to light in a number of aircraft accident/ incident investigations.

Similar to situation awareness, the PIC needs all the inputs to make a correct decision – two heads are always better than one; time permitting though. There may be times when there is no time available and the PIC would then need to take a decision, as he deems fit based on his training and experience. However, when time is available it is best to solicit opinions on the problem; options; pros and cons of each option before taking a decision. Each of these should be weighed in terms of ‘what’ is right, and not ‘who’ is right, under the given set of circumstances. After the decision has been made; and responsibilities assigned to implement the decision, it should be reviewed, and the same process of decision making (DODAR) should continue. This sounds simple but how do we ensure inputs from all sources? This can only happen by empowering the crew.

It is the PIC’s responsibility to empower the crew by facilitating the formation of a team at the earliest opportunity provided. This seems difficult but is actually not so. All crew members on the line are trained, licensed, and proficient to do their jobs well. However, it should be remembered that proficient individuals do not always make competent teams. Our cricket team brings this out clearly. It is the responsibility of the leader, the Commander, to turn these competent individual crew members in to a competent team. The team members are technically qualified, trained and proficient to undertake the flight, and contribute to the task of a safe flight. However, it is the human aspects that need greater attention by each and every PIC before, during, and after the flight to ensure optimum performance from every crew member. A study of past accidents/ incidents points towards a deficiency in this area.

Just thinking of the co-pilot as a ‘Second in Command’, and the cabin crew as additional ‘eyes, ears and brains’ that are available, would help the PIC in finding better ways to making optimum use of all the available human resources within the aircraft itself. In addition, there are other human resources available too via the Radio Telephony. This suggested way of thinking subtly implies that the PIC needs to internalise the fact that each one of his crew in the aircraft, besides others who are outside the aircraft, are making vital contributions to the accomplishment of the common goal of safe flight from A to B, while being assigned seemingly different roles. The contribution of the crew towards the achievement of the common goal should be emphasised, valued, and acknowledged during the first meeting of the crew at the reporting point itself through appropriate behaviours and communicated through words, tone, and body language, so as to create an effective leader/ team relationship.

Research has shown that high performance Captains use three methods to build an effective leader/ team authority relationship. They establish their capability to assume the legitimate authority bestowed on them through law, by establishing competence through a well organised and logical briefing about the specific task at hand – each flight may follow the same routing, but no two flights can ever be the same. Having briefed, they balance the leader/ crew relationship by having the crew members take responsibility for the work of the group as well – this is an important element to empower the other crew members. One Captain is known to have made this statement before an extremely effective crew performance in the simulator: “I just want you guys to understand that they assign seats in this airplane based on seniority, not on the basis of competence. So anything you can see or do which will help out, I’d sure appreciate hearing about it.” Lastly, these Captains interact with humans (emotional beings, unlike robots) who would be filling in different roles on the flight. Crew were encouraged to converse and made to feel comfortable, particularly when conversation was related to the task at hand. Questions and comments were encouraged by all crew members on any aspects of the briefing/ task. By doing this, these Captains had set an authority pattern ranging from the authoritative to consultative, to participative and finally to the democratic. This is what balances the need of a single authority responsible for the safety of the flight with the contributions of all crew members to achieve a safe flight. It is important for the PIC to understand the role of verbal and non verbal communications in the accomplishment of the task. Effective communications before (in the form of a briefing), during (inquiring if something is amiss/ not as planned; advocating one’s own professional opinion, with reasons; etc.), and after the flight (a thorough critique is essential for learning/ team building and growth) is crucial towards effective team work on the aircraft. Effective communications is more likely to result in a situation where the crews are empowered.

The regulator and the company management empower the crew by laying down rules, SOPs and checklists that are required to be followed. The PIC can empower them further by providing them the right leadership, through effective communications, and by communicating, and more importantly by following all laid down SOPs and checklists. As has already been brought out, the leadership style utilised by the PIC would vary from Autocratic (in time critical situations) to Consultative, to Participative, to Democratic. However, it should always be borne in mind that this does not absolve the PIC of any of his responsibilities as laid down by the law. The law gives the PIC the authority, but he needs to earn the respect of his team members by his behaviour. A PIC who respects the others will be respected by the others. The formation of the team starts the moment the individual crew members start assembling at the reporting point.

The Captain must lead by example by following all checklists, laid down procedures and SOPs so that all crew members are on the same page, and know exactly what is being done, and what needs to be done at each stage of the flight. This helps the crew to identify, and point out deviations from the normal, which could be unintentional. Following the Captain’s lead, other crew members would be less tempted to resort to violations or the intentional disregard for laid down procedures. Sterile cockpit procedures are one such procedure that has been violated on a number of flights that have met with accidents or incidents. Sterile cockpit needs to be observed so that our single channel processing brain does not get distracted from the task at hand during crucial phases of flight. The Captain sets the tone for this, and is also responsible to ensure its sanctity by disciplining non conforming crew members.

The workload in the cockpit keeps varying on different crew members during different times/ flights. Workload management is one of the key responsibilities of the Captain. He must ensure that the work load is evenly distributed and that no crew is over or underworked – both situations lead to a drop in the arousal levels and in turn affect the processing capabilities of the brain. High workload leads to stress and fatigue, and its attendant problems, whereas under load leads to boredom, sleepiness, and loss of attention. Low workload situations are encountered during auto-pilot cruise on long flights. The Captain must ensure that the crew continue to monitor the systems for correct functioning. Even when the aircraft is on autopilot, the PF is responsible to ensure that the flight is on the desired trajectory and the systems are functioning as designed. The PM (PNF) must monitor any changes, even when engaged in non critical activities like flight plan, tuning, communications, etc. The standard dictum of flight prioritisation viz., ‘Aviate, Navigate and communicate’ should be followed.

High or low workload, it is a known fact that a highly motivated individual performs better under all conditions. Motivating pilots is relatively simple because most love their job – it is easier to motivate an individual who loves his job, as the motivator is in the job content itself. The Commander should try and provide opportunities for the crew to grow, of course within the laid down regulations. This is very motivating for the crew and the performance of the team improves. Mentoring a relatively inexperienced crew member pays rich dividends in terms of motivation and job satisfaction for both the mentor and the mentee.

Having gone through this paper, one is tempted to ask, “So what is CRM?” It is nothing but understanding that aviation is a complex system; we are human in that our physical, physiological and psychological performance keeps changing and that our information processing system has serious limitations (specially under time critical situations); that humans are emotional beings; that we need all the help possible to fly safely from A to B; that it is humanly not possible to do things by ourselves and that other crew members can be a big help, but would need to be led, motivated, involved to bring out their most optimum performance. Past accidents provide evidence that technical competence is an important requirement, but not the only requirement for safe operations; interpersonal and cognitive (information processing has severe limitations, especially under time critical situations) functions also have to be integrated in to flight operations to achieve a safe flight.

Finally, CRM is a concept that recognises the critical role of human factors in determining the effectiveness of technically proficient crew in both normal and non normal situations and gives one a practical approach which can help in an attitudinal/ behavioural change so that competent individuals can come together to form a competent team.

How does one recognise a competent team from just a technically proficient team? A competent team is one that can operate a safe and efficient flight from A to B, and also terminate the flight with the crews deriving satisfaction from working as valued professional members of the team, and also with a readiness/ willingness to perform together as a crew in the future.

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