We have compiled some relevant information below. There are links to full articles and GAPs here too, and you will find more information on the CAA website.
Whatever you are flying – a hang glider, a paraglider, a glider, a microlight, a helicopter, or an airliner – you must know the limits of your aircraft. When combined with a sound knowledge of the way forces act on your aircraft, you should be able to operate within your aircraft limits at all times.
Principles of Flight
Any time an aircraft is airborne, it is subject to at least three forces: lift, drag, and weight. An aircraft under power will also be subject to thrust. In stable level flight, these will be balanced, which also includes any tailplane force required to balance pitching moments. Lift will be equal to the aircraft weight, plus or minus (normally plus) the tailplane force. This tailplane force is normally much less than the lift force, so the lift and weight can be considered equal.
The Four Forces
The heavier the aircraft the more lift required to maintain level flight.
The heavier the aircraft the greater the load imposed on the airframe.
The extra lift required at heavier weights means that more drag will also be generated. So the heavier the aircraft gets, the faster it tends to slow down. This may be your only direct indication of increased loading.
A heavier aircraft flying in turbulence will also tend to ride better, since it will respond less to a given gust, again giving the impression of a smoother ride and less stress to the airframe. This is quite wrong. While the response to turbulence is reduced, the actual loads on the airframe will increase. Compare an empty trailer to one full of sand, going over pot holes. The full trailer bounces a lot less but is subject to much more loading.
Load Factor and G Limits
The ratio of lift produced to aircraft weight is called the load factor, and it is a measure of the acceleration in the direction of the manoeuvre.
The pilot perceives this load factor as the G-force experienced.
In a 60-degree turn, the lift is twice the weight, making the load factor 2, or 2-G.
These limits are found in the Aircraft Flight Manual and relate to the aircraft at its maximum all up weight (MAUW). You can fly at the ‘limit load’ without any resultant deformation of the aircraft. Beyond this – normally by another 50 percent – is the ‘ultimate load’, at which point the aircraft structure has been calculated to fail. Between the limit load and ultimate load, some deformation or damage to the aircraft can be expected. The ‘buffer’ is there to allow for miscalculations by designers, manufacturing defects, and ageing aircraft – not for pilots to help themselves to.
Whenever the aircraft is manoeuvred, the lift required changes.
As we said above, an aircraft in a 60-degree angle of bank turn experiences a load factor of 2. Effectively your aircraft (and everything in it) now weighs twice its original weight.
In order for the wings to provide that additional lift, the angle of attack is increased, and an increased angle of attack results in increased drag (induced drag increases by about 300 percent in this situation) and a reduced airspeed (unless you add power).
With weight effectively increased in the turn, the stall speed increases, because stall speed increases with increasing weight.
In addition, when aileron is applied to roll the aircraft, the up-going wing is producing more lift than the down-going wing. It is therefore possible to exceed the design strength of the up-going wing while still below the overall aircraft limits. This can be achieved by applying aileron when G is already applied – known as ‘rolling G’ – or in some cases simply by applying aileron at high speed. Be cautious about application of aileron whenever under G or at high speeds.
When the aircraft is turning, you are increasing the stress on the airframe. Turbulence increases that stress even further, so rolling the aircraft into a steep turn while yanking back on the control column may just rip its wings off.
The Manoeuvre Envelope (VN diagram)
A simple way of presenting this data is by using the VN diagram. This is a graph of G against speed. Together, speed and G limits provide the ‘flight envelope’ of the aircraft: what it is allowed to do, what it cannot physically do, and what it should not do. Anything outside the envelope is beyond the limit load the airframe was designed for.
Know Your Limits
Some microlights and some amateur-built aircraft have very little information available on their speed and G-limits. It is up to you to know these limits and there are a couple of ways you can find them if they are not included in the operating manual. You might like to try the designer’s web site. Alternatively you could contact the designer directly. Another option is to contact your national organisation, such as the SAA or Part 149 organisation.
Full Vector article on aerodynamic limits is here.
Maximum Rate Turns
This is a summary of the briefing for maximum rate turns from the Flight Instructor Guide.
To achieve the maximum rate of turn, the greatest possible force toward the centre of the turn is required. This is achieved by inclining the lift vector as far as possible. Therefore, maximum CL, achieved at the maximum angle of attack, is combined with the maximum angle of bank.
The maximum rate of turn occurs when the aeroplane is changing direction at the highest possible rate, ie, maximum degrees turned through in minimum time (rate of change of direction).
For the purposes of collision avoidance, in response to an emergency situation, the turn entry requires a rapid roll-in. However, the roll out is smoothly executed because the emergency is over.
As an exercise, the rapid-roll in and smooth roll out provide excellent coordination practise, because two different rates of rudder and elevator application are required to match the rate of roll. Logically these turns would not be continued past 180 degrees in the case of collision avoidance. To improve coordination and orientation, however, the maximum rate turn is commonly practised through 360 degrees.
Principles of Flight
Lift varies with angle of attack and airspeed. The highest useful angle of attack is just before the critical angle, about 15 degrees. At this high angle of attack, maximum CL, considerable drag is produced, and if the aeroplane stalls, or the buffet is reached, the drag will increase dramatically. Ideally, sufficient backpressure should be applied to activate the stall warning (if it is operating) on its first note. Alternatively, the very edge of the buffet will need to be used as a guide to maximum CL.
The speed we are particularly interested in is VA.
VA is the maximum speed at which the pilot can make abrupt and extreme control movements and not overstress the aeroplane’s structures. Above VA and the aeroplane can be overstressed before it stalls. Below VA. the aeroplane will stall before it is overstressed.
This is a particularly important consideration if the nose is allowed to drop during steep turns, and the pilot pulls back harder on the control column to regain the height. The correct recovery technique is to reduce the angle of bank before increasing the back pressure.
VA is determined by multiplying the basic stall speed by the square root of the maximum load factor. Practically, the speed will be found in the Flight Manual.
VA is affected by the aeroplane’s weight and reduces as weight reduces. This is because a heavier aeroplane will take longer to respond to a full control deflection than a lighter aeroplane. The quick response of the lighter aeroplane results in higher loading. Therefore, as the weight of the aeroplane is reduced, the speed at which full and abrupt control movements can be made is also reduced (refer Flight Manual).
Rate of Turn and Radius of Turn
Rate of turn is the rate of change of direction, that is, how many degrees are turned through in a specific time, usually a minute.
Radius of turn is the size of the arc made by the aeroplane as it turns.
A low speed means a higher rate of turn; a higher forward speed means a lower rate of turn.
A high speed allows you to generate more lift and therefore use an increased angle of bank, but the high airspeed means the radius of the turn (how many nautical miles it takes to make the turn) is high and therefore the rate will be lower.
To turn at maximum rate, we need maximum centripetal force and maximum lift. The increased angle of attack means increased drag, so full power is used. As rate of turn is proportional to velocity, the limiting factor in a maximum rate turn is power.
If speed is below VA at entry, full power can be used before rolling into the turn. If speed is at VA full power can be applied in conjunction with the roll. When speed is above VA, roll into the turn first and then apply power, so as not to exceed VA.
To make a maximum rate turn you need to turn at the highest angle of bank that can be sustained at the lowest possible airspeed – just above VS – this is why the stall warning is used to indicate maximum rate.
This diagram shows the relationship of load factor to increasing angle of bank. The structural load limit for the aeroplane will determine the maximum angle of bank that could be used without structural failure.
Angle of Bank Limit
An increase in angle of bank requires an increase in the angle of attack to increase the lift, which in turn increases the drag, adversely affecting the L/D ratio, resulting in a decrease in airspeed.
Power is used to oppose the increase in drag. However, since power available is limited, the airspeed will reduce as the angle of bank increases.
The stalling speed increases as the square root of the load factor. With a basic stall speed of 50 knots, 75 degrees angle of bank increases the stall speed to approximately 100 knots. Even if there were no drag increase this would be about the normal cruise speed.
Therefore, the maximum angle of bank will also be limited by the amount of power available to overcome the increasing drag. For most light training aeroplanes, this is the limiting factor at about 60 degrees angle of bank. With the amount of power available, the highest possible speed that can be maintained is a stall speed well below VA (about a 40 percent increase over the basic stall speed). However, it is not necessarily the only limiting factor, as a light twin-engine aeroplane or high performance single may well have sufficient power to combat the increased drag and maintain or exceed VA. Commonly, in this case the aeroplane’s structural limitations limit the maximum angle of bank.
If the airspeed is above VA for the weight, the entry must employ a smooth roll in. Generally, the application of power is delayed until the aeroplane decelerates to VA. Then, power is applied as required to counter the increasing drag in an effort to maintain VA (for the weight).
This would be any airspeed around the stall speed for 60 degrees angle of bank (VS plus about 40 percent, eg, 50 knots plus 40 percent = 70 knots).
In this case, power should lead the roll-in or be applied rapidly but smoothly as soon as the roll-in is started.
The aeroplane’s VA speeds at all up weight and empty (if given in the Flight Manual) are most relevant to this exercise. A stall, or the use of abrupt control movements to initiate the entry, must be avoided above this speed.
For light training aeroplanes, the increase in drag will require that maximum power is used – do not exceed the rpm limit.
The aeroplane’s C of G limitations for the normal and utility categories may be revised.
Disorientation is minimised by choosing a very prominent reference point.
With an increasing positive load factor or G, the heart has more difficulty pumping blood to the brain. Because the eyes are very sensitive to blood flow, the effects of increasing G on vision are noted.
During the maximum rate turn, in most light training aeroplanes, the increased G would not be expected to exceed +2 G.
These effects vary between individuals and are affected by physical fitness, regular exposure and anti-G manoeuvres or devices, for example, straining, or the use of a G-suit.
A reference altitude and very prominent reference point are chosen and the lookout completed.
A check is made to establish where the aeroplane’s speed is, in relation to VA for the aeroplane’s weight. For most light training aeroplanes the airspeed will be about 10 to 20 knots below VA when entering the maximum rate turn from level flight.
Assuming the airspeed is below VA, full power is applied and the aeroplane is rolled rapidly, but smoothly, into the turn with aileron, and balance maintained by applying rudder in the same direction as aileron. As large deflections of aileron are used, more rudder than usual will be required to overcome adverse yaw.
Backpressure is increased on the control column to keep the nose attitude level relative to the horizon, pulling smoothly to the stall warning (or light buffet) to maximise lift.
When the stall warning is activated, maintain backpressure and hold the angle of bank to maintain height. This will be recognised through attitude and confirmed through instruments, a slight check will be required to overcome inertia in roll and rudder pressure will need to be reduced to maintain balance.
If the very rapid roll-in is preferred (for a true avoidance turn rather than a coordination exercise), the initial angle of bank must not exceed the angle of bank at which the structural limits are reached.
Maintaining the Turn
Maintaining the turn incorporates the LAI (lookout – attitude – instruments) scan. Emphasise lookout, and maintain the attitude for CLmax and level flight.
During the turn, maintain the maximum amount of lift for the airspeed by maintaining the first note of the stall warning with backpressure.
As the lift cannot be increased any further, the altitude is maintained with angle of bank. Therefore, with the stall warning activated, if altitude is being gained or lost, alter the angle of bank.
Look into the turn for traffic and the reference point, and allow for inertia by anticipating about 30 degrees before (half the angle of bank), and roll out smoothly.
Smoothly roll wings level with aileron, balance with rudder in the same direction to overcome adverse yaw, and relax the backpressure to re-select the level attitude. Most low-powered training aeroplanes require the reduction of power to be delayed on exiting the maximum rate turn.
Full briefing on FIG website here.
Mountain Flying GAP booklet here.
Dual Flight Training Review
The 2014 CAA project to review the spate of dual flight training accidents is ongoing but has produced an interim report based on its findings so far. There were 27 identifiable areas of concern showing one overarching theme with four major subsets.
The overarching theme is accountability.
The four subsets are: Supervision, Training Model, Record Keeping and Type Ratings.
Supervision was found to be generally poor in two areas: organisation supervision of instructors, and instructor supervision of their students. The question arises of which A or B Cat is supervising which C Cat? It is difficult to find evidence of the direct supervision of C Cat instructors for the first six months/100 hours (whichever comes last) or the subsequent indirect supervision of C Cats.
Smaller organisations appear to have more 'ownership' of their instructors and students. Larger organisations seem to use their pool of instructors on an ad-hoc basis making identification of supervising instructor difficult, with students not being allocated to nominated individual instructors. The instructor suffers from not being mentored and the student suffers from a lack of continuity. This manifests itself as an inefficient utilisation of training hours, usually to the detriment of the student.
- Supervision of instructors must be transparent, documented and meaningful.
- Each student pilot must have just one instructor responsible for them and that instructor should only have a small group of students.
- Instructors presenting candidates for examination should attend the debriefing to understand where to focus the future training and preparation.
- Instructors must take ownership of their candidate and sign the logbook to indicate their student has completed the training and the instructor has assessed them as competent to sit this test.
- Junior instructors must be resourced; ie, qualified, competent and capable of completing the task.
This is in some ways a subset of supervision. Training models should reflect the best of teaching practice and follow a logical, structured sequence of development. It was found this is not always the case, evidenced by significant time having been flown yet specific eligibility requirements show only the bare minimum hours, that is, minimum syllabus hours requirements become maximum aiming points.
Most of the instructors involved in the accidents have suffered through models that showed multiple instructors; lacked targeted consolidation; had incomplete syllabus coverage; showed poor administration of students through the course; demanded multiple objectives in a single flight; lacked set objectives for solo flights; and showed a lack of 'ownership' of students by instructors.
- Flight training organisations need to model good instructional technique by having established a sound course syllabus, provided all necessary course material and facilities, and have competent instructors available.
- Flight training programmes need to be managed and supervised by the organisation. Timely interventions and active student participation in their progress must be encouraged.
- New C-Cats should be given a dedicated student through a complete course, because instructors need to learn the responsibility of having a student's future in their hands.
- Organisations must do a needs-assessment after a student or instructor has had a break from flying, to ensure that they are competent to progress.
- Solo flights must have specific assigned objectives for student pilots to achieve.
- Circuit consolidation of five hours post solo must be completed.
- The training model must ensure all syllabus content is covered and is documented in the training records.
- Advisory Circular cross-country syllabus requirements are to be met.
The lack of record keeping is quite disturbing. Training records in some organisations were incomplete or inaccurate, or contained scant detail of the personal details expected. Flight reports were often cursory, consisting of scrawled notes or ticks in boxes without any elaboration. There was a lack of clearly detailed or defined flight training process. A student should be able to review their progress towards a licence or rating through their records but this is often not the case.
Finally, but by no means least important, is the lack of administration of personal logbooks. These are often incomplete or not up to date.
- Ensure logbooks are supervised and correctly completed.
- Training records must be supported by logbook entries, in addition the organisation records need to show ground and flight training details.
- Signatures in logbooks show legal accountability, so instructors should only sign for what they know to be true.
- Record flight test fails in both the logbook as well as training records.
Flight rating requirements are reasonably well documented in Part 61 and AC61-10. During the investigations it was found that flying time is often short of the minimum specified. Short flying times for complex aircraft initial type ratings, in particular, set people up for problems in future flight. There was a general lack of type rating training in MAUW operations and a lack of PIC/solo time before sign off.
All of these issues lead to poor performance as newly type-rated pilots struggle to cope with operations that should have been covered in type rating training. A type rating gives the right to exercise privileges and so should be properly completed.
- Minimum standards are not a target; the minimum prescribed time for type rating in the advisory circular is not to be considered a maximum
- Ensure type rating training is conducted to a standard to exercise privileges.
- Competency is the driver not flying time or cost.
Has the organisation done its best? Is the CEO prepared to stand in front of a coroner and state their organisation has done its best?
Is the primary supervisor prepared to say they effectively supervised and mentored the C-Cat through their direct supervision period?
Is the instructor prepared to sign they have delivered all the training required and the student is fully competent to sit the test?
Is the examiner prepared to say they have examined all the paperwork presented for the flight test and not proceed if the requirements have not been met?
Everyone with an active role in the flight training system holds accountability to a greater or lesser extent for the performance of the system. Are you playing your part?
Full related Vector article here.