4: Preflight Considerations

Introduction

Determining Speed and Altitude

Loading

Load Factor

Stalls

Performance

Physiology

Maintenance and Inspection Procedures

Introduction

The remote PIC is responsible for ensuring the sUAS is in a condition for safe operation. Part of this involves checking for proper loading, so that the device operates to the expected performance standards.

Prior to each flight, the remote PIC must ensure that any object attached to or carried by the small unmanned aircraft is secure and does not adversely affect the flight characteristics or controllability of the aircraft. For example, some sUA do not have a set holder or slot for the battery; instead, it is simply attached with hook-and-loop or other type of fastener. This allows some leeway on the lateral and longitudinal location of the battery on the sUA. Remote pilots should ensure the battery is installed in the proper location so it does not adversely affect the controllability of the aircraft. The attachments must be secure so the battery does not move during flight. Similar concerns exist and cautions advised if any external attachments are installed. Also be sure to close and lock (if applicable) all panels or doors.

Follow all manufacturer recommendations for evaluating performance to ensure safe and efficient operation. This manufacturer information may include operational performance details for the aircraft such as launch, climb, range, endurance, descent, and landing. It is important to understand the significance of the operational data to be able to make practical use of the aircraft’s capabilities and limitations. The manufacturer’s information regarding performance data is not standardized; availability and how this information is conveyed can vary greatly between sUAS types. If manufacturer-published performance data is unavailable, the remote pilot should seek out performance data that may have already been determined and published by other users of the same sUAS manufacturer model, and use that data as a starting point.

Check weather conditions prior to and during every sUAS flight and consider the effects of weather on aircraft performance.

Airplane flight control systems consist of primary and secondary systems. The ailerons, elevator (or stabilator) and rudder constitute the primary control system and are required to control an airplane safely during flight. Wing flaps, leading edge devices, spoilers and trim systems constitute the secondary control system and improve the performance characteristics of the airplane or relieve the pilot of excessive control forces. See Figure 4-1.

Figure 4-1. Aircraft flight controls

A helicopter has four flight control inputs: cyclic, collective, antitorque pedals, and throttle. The cyclic can vary the pitch of the rotor blades throughout each revolution of the main rotor system to develop lift (thrust). The result is to tilt the rotor disc in a particular direction, resulting in the helicopter moving in that direction.

Determining Speed and Altitude

The remote pilot must not exceed these regulatory limitations for operating an sUAS:

Some of the possible ways to ensure that 87 knots is not exceeded include:

These navigation terms are used in aviation as related to ground speed:

Some possible ways for a remote pilot to determine altitude above the ground or structure are as follows:

In addition to local resources, the Sectional Chart for that region should be consulted for information on the altitude of the terrain and structures. Towers and other known obstructions are depicted with their altitude noted. It is critical to understand that altitude dimensions of airspace depicted on Sectional Charts are in MSL; remote pilots must be careful to properly convert between AGL and MSL as applicable to their equipment, operation, and regulation restrictions. See Legend 1 in the CT-8080-2.

Loading

As with any aircraft, compliance with weight and balance limits is critical to the safety of flight for sUAS. An unmanned aircraft that is loaded out of balance may exhibit unexpected and unsafe flight characteristics. An overweight condition may cause problematic control or performance limitations. Before any flight, verify that the unmanned aircraft is correctly loaded by determining the weight and balance condition.

Although a maximum gross launch weight may be specified, the aircraft may not always safely take off with this load under all conditions. Or if it does become airborne, the unmanned aircraft may exhibit unexpected and unusually poor flight characteristics. Conditions that affect launch and climb performance, such as high elevations, high air temperatures, and high humidity (high density altitudes) as well as windy conditions may require a reduction in weight before flight is attempted. Other factors to consider prior to launch are runway/launch area length, surface, slope, surface wind, and the presence of obstacles. These factors may require a reduction in weight prior to flight.

Weight changes during flight also have a direct effect on aircraft performance. Fuel burn is the most common weight change that takes place during flight. As fuel is used, the aircraft becomes lighter and performance is improved, but this could have a negative effect on balance. For battery-powered sUAS operations, weight change during flight may occur when expendable items are used on board (e.g., a jettisonable load such as an agricultural spray). Changes of mounted equipment between flights, such as the installation of different cameras, battery packs, or other instruments may also affect the weight and balance and performance of an sUAS.

Adverse balance conditions (i.e., weight distribution) may affect flight characteristics in much the same manner as an excess weight condition. Limits for the location of the CG may be established by the manufacturer and may be covered in the pilot operating handbook (POH) or sUAS flight manual. The CG is not a fixed point marked on the aircraft; its location depends on the distribution of aircraft weight. As variable load items are shifted or expended, there may be a resultant shift in CG location. The remote PIC should determine how the CG will shift and the resultant effects on the aircraft. If the CG is not within the allowable limits after loading or do not remain within the allowable limits for safe flight, it will be necessary to relocate or shed some weight before flight is attempted.

Excessive weight reduces the flight performance in almost every respect. In addition, operating above the maximum weight limitation can compromise the structural integrity of an sUA. The most common performance deficiencies of an overloaded aircraft are:

Prior to conducting a mission or extended flight, it is recommended to test-fly the sUA to determine if there are any unexpected performance issues due to loading. This testing should be done away from obstacles and people.

Computing Weight and Balance

The empty weight is obtained from manufacturers’ documentation. It includes the airframe, power source, all fixed equipment, and unusable fuel. The useful load includes the power source (battery or fuel) and payload or mission equipment (such as a camera). The launch weight is the empty weight plus the useful load. The landing weight is the launch weight minus any fuel used or jettisoned load.

The arm is the horizontal distance measured in inches from the datum line (a reference point along the longitudinal axis indicated by the manufacturer) to a point on the sUAS. If measured aft, toward the defined rear of the aircraft, the arm is given a positive (+) value; if measured forward, toward the defined front, the arm is given a negative (-) value.

The moment is the product of the weight of an object multiplied by its arm and is expressed in pound-inches (lbs-in). The moment is essentially a force being applied at a location along the longitudinal axis, which must be countered by the control capabilities of the aircraft. If moment(s) exceed the control capacity of the aircraft, it becomes unstable or uncontrollable. The formula that is used to find moment is usually expressed as follows: Weight × Arm = Moment.

The CG is the point about which an aircraft will balance, and it is expressed in inches from datum. The CG is found by dividing the total moment by the total weight, and the formula is usually expressed as follows: Total Moment = CG (inches aft of datum) / Total Weight.

Lateral CG is also important (measured along the horizontal axis). Uneven distribution of weight on one side of the aircraft versus the other may cause controllability and/or performance issues.

Load Factor

In aerodynamics, load is the force or imposed stress that must be supported by an sUA structure in flight. The loads imposed on the wings or rotors in flight are stated in terms of load factor. In straight-and-level flight, the sUAS wings/rotors support a load equal to the sum of the weight of the sUAS plus its contents. This particular load factor is equal to 1 G, where “G” refers to the pull of gravity. However, centrifugal force is generated which acts toward the outside of the curve any time an sUAS is flying a curved path (turns, climbs, or descents).

Unmanned aircraft performance can be decreased due to an increase in load factor when the aircraft is operated in maneuvers other than straight and level flight. The load factor increases at a significant rate after a bank (turn) has reached 45° or 50°. The load factor for any aircraft in a coordinated level turn at 60° bank is 2 Gs. The load factor in an 80° bank is 5.75 Gs. See Figure 4-2. The wing must produce lift equal to these load factors if altitude is to be maintained. The remote PIC should be mindful of the increased load factor and its possible effects on the aircraft’s structural integrity and the results of an increase in stall speed. These principles apply to both fixed-wing and rotor-wing designs, but in the case of rotor-wing unmanned aircraft, the weight/load must be supported by the lift generated by the propellers.

Figure 4-2. Load factor chart

As with manned aircraft, an unmanned aircraft will stall when critical angle of attack of the wing or rotors/propeller is exceeded. This can occur when an unmanned aircraft is turned too sharply/tightly or pitched up too steeply or rapidly. Remote pilots of rotor type unmanned aircraft should use particular caution when descending in a vertical straight line. In some cases, the turbulent downward airflow can disrupt the normal production of lift by the propellers as well as cause problematic air circulation producing vortices. These phenomena are referred to as vortex ring state or settling with power, and when they occur the aircraft can wobble, descend rapidly, or become uncontrollable. Recovery from this state of flight requires forward or rearward motion—counterintuitively, the addition of power to arrest the descent only makes the situation worse. Due to the low-altitude operating environment, consideration should be given to ensure aircraft control is maintained and the aircraft is not operated outside its performance limits.

Stalls

An airfoil is a structure or body that produces a useful reaction to air movement. Airplane wings, helicopter rotor blades, and propellers are airfoils. The chord line is an imaginary straight line from the leading edge to the trailing edge of an airfoil. In aerodynamics, relative wind is the wind “felt” or experienced by an airfoil. It is created by the movement of air past an airfoil, by the motion of an airfoil through the air, or by a combination of the two. Relative wind is parallel to, and in the opposite direction of the flight path of the airfoil. The angle of attack is the angle between the chord line of the airfoil and the relative wind. Angle of attack is directly related to the generation of lift by an airfoil. See Figures 4-3 through 4-6.

Figure 4-3. A typical airfoil cross-section

Figure 4-4. Chord line

Figure 4-5. Relative wind

Figure 4-6. Angle of attack

As the angle of attack is increased (to increase lift), the air will no longer flow smoothly over the upper airfoil surface but instead will become turbulent or “burble” near the trailing edge. A further increase in the angle of attack will cause the turbulent area to expand forward. At an angle of attack of approximately 18° to 20° (for most airfoils), turbulence over the upper wing surface decreases lift so drastically that flight cannot be sustained and the airfoil stalls. See Figure 4-7. The angle at which a stall occurs is called the critical angle of attack. An unmanned aircraft can stall at any airspeed or any attitude, but will always stall at the same critical angle of attack. The critical angle of attack of an airfoil is a function of its design therefore does not change based upon weight, maneuvering, or density altitude. However, the airspeed (strength of the relative wind) at which a given aircraft will stall in a particular configuration will remain the same regardless of altitude.

Figure 4-7. Flow of air over wing at various angles of attack

Because air density decreases with an increase in altitude, an unmanned aircraft must have greater forward speed to encounter the same strength of relative wind as would be experienced with the thicker air at lower altitudes. An easier way to envision this concept is to imagine how many molecules of air pass over an airfoil per second—thicker air at lower altitudes has more air molecules for a given area than the thinner air at higher altitudes. In order to successfully keep an aircraft aloft, a minimum number of air molecules must pass over the airfoil per second. As fewer molecules are available to make the journey as altitude increases, the only way to ensure that the aircraft can stay aloft is to increase its forward speed, thus forcing more air molecules over the airfoil each second.

Performance

Performance or operational information may be provided by the manufacturer in the form of pilot’s operating handbook, owner’s manual, or on the manufacturer’s website. Follow all manufacturer recommendations for evaluating performance to ensure safe and efficient operation. Even when specific performance data is not provided, the remote PIC should be familiar with:

Even when operational data is not supplied by the manufacturer, the remote PIC can better understand the unmanned aircraft's capabilities and limitations by establishing a process for tracking malfunctions, defects, and flight characteristics in various environments and conditions. Use this operational data to establish a baseline for determining performance, reliability, and risk assessment for your particular system.

The remote PIC is responsible for ensuring that every flight can be accomplished safely, does not pose an undue hazard, and does not increase the likelihood of a loss of positive control. Consider how your decisions affect the safety of flight. For example:

Due to the diversity and rapidly evolving nature of sUAS operations, individual remote PICs have flexibility to determine what equipage methods, if any, mitigate risk sufficiently to meet performance-based requirements, such as the prohibition against creating an undue hazard if there is a loss of aircraft control.

Physiology

Remote pilots are not required to hold a medical certificate. However, no person may manipulate the flight controls of an sUAS or act as a remote PIC, VO, or direct participant in the operation of the sUA if he or she knows or has reason to know that he or she has a physical or mental condition that would interfere with the safe operation of the sUAS. Remote pilots must self-assess their fitness for flight. Pilot performance can be seriously degraded by a number of physiological factors. While some of the factors may be beyond the control of the pilot, awareness of cause and effect can help minimize any adverse effects. At any time a remote PIC determines that they or another crewmember is unfit to operate the sUAS or participate in its operation, the remote PIC should terminate the operation and/or follow contingency plans for such occasions (e.g., incapacitation).

Hyperventilation, a deficiency of carbon dioxide within the body, can be the result of rapid or extra deep breathing due to emotional tension, anxiety, or fear. Symptoms will subside after the rate and depth of breathing are brought under control. A pilot should be able to overcome the symptoms or avoid future occurrences of hyperventilation by talking aloud, breathing into a bag, or slowing the breathing rate.

The sUAS operating environment can be very extreme for crewmembers. It is not uncommon for sUAS operations to take place in hot, dry and dusty locations, which can lead to dehydration and/or heat stroke. Alternatively, sUAS also operate in cold or other conditions that leave crewmembers exposed to the elements that could lead to dehydration and hypothermia. Dehydration is the term given to a critical loss of water from the body. Causes of dehydration are environmental conditions, wind, humidity, and diuretic drinks (i.e., coffee, tea, alcohol, and caffeinated soft drinks). Some common signs of dehydration are headache, fatigue, cramps, sleepiness, and dizziness. To help prevent dehydration, drink two to four quarts of water every 24 hours.

Heatstroke is a condition caused by any inability of the body to control its temperature. Onset of this condition may be recognized by the symptoms of dehydration, but also has been known to be recognized only upon complete collapse.

Hypothermia is indicated by shivering, clumsiness, slurred speech, confusion, low energy, discoloration of the skin (red or blue), and loss of consciousness. Remote PICs should ensure that they and their fellow crewmembers are adequately prepared for the planned sUAS operation and the environment in which this operation is set to take place. Some things to keep in mind are: providing ample water or other hydrating beverages, eye protection, sun protection, insect repellent, warm clothes or clothes suited for heat (whichever is appropriate), support equipment, and any other items deemed necessary for safety and comfort.

Stress is ever present in our lives and you may already be familiar with situations that create stress in aviation. However, sUAS operations may create stressors that differ from manned aviation. Such examples may include: working with an inexperienced crewmember, lack of standard crewmember training, interacting with the public and government officials, and understanding new regulatory requirements. Proper planning for the operation can reduce or eliminate stress, allowing you to focus more clearly on the operation.

Fatigue is frequently associated with pilot error. Some of the effects of fatigue include degradation of attention and concentration, impaired coordination, and decreased ability to communicate. These factors seriously influence the ability to make effective decisions. Physical fatigue results from sleep loss, exercise, or physical work. Factors such as stress and prolonged performance of cognitive work can result in mental fatigue. Fatigue falls into two broad categories: acute and chronic. Acute fatigue is short term and is a normal occurrence in everyday living. It is the kind of tiredness people feel after a period of strenuous effort, excitement, or lack of sleep. Rest after exertion and 8 hours of sound sleep ordinarily cures this condition. Chronic fatigue is characterized by extreme fatigue or tiredness that doesn’t go away with rest, and can’t be explained by an underlying medical condition. Chronic fatigue can also occur when there is not enough time for a full recovery from repeated episodes of acute fatigue.

Chronic stress results with longer-term stresses and/or the mismanagement thereof and can result in serious health conditions such as anxiety, high blood pressure, a weakened immune system, depression, confusion, mental errors, insomnia, and memory loss. The best way to cope with chronic stress is to remove stressors as much as practical, take part in physical activity, and/or seek out the advice or care of a healthcare provider.

Vision is the most important body sense for safe flight. Major factors that determine how effectively vision can be used are the level of illumination and the technique of scanning the sky for other aircraft. Atmospheric haze and fog reduces the ability to see traffic or terrain during flight, making all features appear to be farther away than they actually are. Caution is always advised in areas of reduced visibility or low light.

Additionally, the remote PIC and crewmembers should take into account the impact the environment may have on vision, such as location and angle of the sun, the color and texture of the local terrain features, as well as glare from water, buildings, or other objects. Particular caution is advised when operating near terrain features which may make it difficult to distinguish the sUAS from the surrounding environment or may make it difficult to ascertain proper depth perception (e.g., terrain colors similar to the sUA or a large area of trees which may make it more challenging to determine the distance between the unmanned aircraft and the foliage).

Maintenance and Inspection Procedures

Maintenance for sUAS includes scheduled and unscheduled overhaul, repair, inspection, modification, replacement, and system software upgrades for the unmanned aircraft itself and all components necessary for flight.

Manufacturers may recommend a maintenance or replacement schedule for the unmanned aircraft and system components based on time-in-service limits and other factors. Follow all manufacturer maintenance recommendations to achieve the longest and safest service life of the sUAS. If the sUAS or component manufacturer does not provide scheduled maintenance instructions, it is recommended that you establish your own scheduled maintenance protocol. For example:

During the course of a preflight inspection, you may discover that an sUAS component requires some form of maintenance outside of the scheduled maintenance period. For example, an sUAS component may require servicing (such as lubrication), repair, modification, overhaul, or replacement as a result of normal or abnormal flight operations. Or, the sUAS manufacturer or component manufacturer may require an unscheduled system software update to correct a problem. In the event such a condition is found, do not conduct flight operations until the discrepancy is corrected.

In some instances, the sUAS or component manufacturer may require certain maintenance tasks be performed by the manufacturer or by a person or facility specified by the manufacturer; maintenance should be performed in accordance with the manufacturer’s instructions. However, if you decide not to use the manufacturer or the personnel recommended by the manufacturer and you are unable to perform the required maintenance yourself, you should:

If you or the maintenance personnel are unable to repair, modify, or overhaul an sUAS or component back to its safe operational specification, then it is advisable to replace the sUAS or component with one that is in a condition for safe operation. Complete all required maintenance before each flight—preferably in accordance with the manufacturer’s instructions or, in lieu of that, within known industry best practices.

Careful recordkeeping can be highly beneficial for sUAS owners and operators. For example, recordkeeping provides essential safety support for commercial operators who may experience rapidly accumulated flight operational hours/cycles. Consider maintaining a hardcopy and/or electronic logbook of all periodic inspections, maintenance, preventative maintenance, repairs, and alterations performed on the sUAS. See Figure 5-6. Such records should include all components of the sUAS, including the:

Figure 4-8. A UAS logbook can be used to track remote pilot hours as well as sUAS maintenance

[10-2024]