Trailing cone

A trailing cone is a calibration apparatus employed in aviation flight testing to accurately measure ambient static air pressure by deploying a lightweight, cone-shaped device trailed behind an aircraft on a flexible cable, which positions the pressure sensors in undisturbed airflow far from the aircraft's aerodynamic influences.^[1] This method corrects for static position errors in the aircraft's pitot-static system, ensuring precise determinations of airspeed, altitude, and Mach number across various flight conditions.^[2] Developed in the mid-20th century as an economical alternative to more complex calibration techniques, the trailing cone concept evolved from earlier static pressure measurement devices, with initial prototypes tested in the 1950s and refined through wind tunnel and in-flight evaluations by organizations including the U.S. Navy and NASA in the 1960s.^[3] The device typically consists of a fiberglass or similar lightweight cone, approximately 12.7 cm in base diameter, attached to a high-strength tubing system that includes pressure orifices located 5 to 6 cone diameters ahead of the cone's base to capture static pressure while the cone provides aerodynamic stability through drag.^[1] During operation, the cone is reeled out to a distance of at least one fuselage length—often 100 to 200 feet—behind the aircraft, where it aligns with the local airflow regardless of the aircraft's angle of attack, allowing direct comparison between the trailed pressure reading and the onboard static ports.^[3] Trailing cones have been validated in subsonic and transonic wind tunnel tests up to Mach 0.95, demonstrating pressure measurement accuracies within 0.001 Mach number, with minimal sensitivity to Reynolds number variations or protective modifications like skids.^[1] In flight applications, they have supported position error calibrations for research and survey aircraft, reducing errors to as low as 0.3 mb (about 0.63 psf) at altitudes up to 40,000 feet and speeds exceeding Mach 1.0, proving effective in unaccelerated level flight across diverse aircraft types.^[4] Though primarily used during certification and developmental testing, the trailing cone remains a reliable tool for high-precision air data calibration, particularly where advanced instrumentation like trailing bombs or GPS-aided methods are impractical.^[2]

Overview and Principles

Definition and Purpose

A trailing cone is a lightweight, aerodynamic probe consisting of a cone-shaped device towed behind an aircraft via a flexible, high-strength tube to measure undisturbed static pressure in the freestream airflow.^[1]^[5] This system serves as a specialized tool for obtaining precise atmospheric pressure data far removed from the aircraft's aerodynamic disturbances, such as boundary layers or shock waves that affect onboard sensors.^[3] The primary purpose of the trailing cone is to provide precision calibration for aircraft static pressure systems, which are essential for accurate determinations of airspeed, altitude, and Mach number, particularly in high-speed or transonic flight regimes where fuselage-mounted static ports experience significant distortions from local airflow effects.^[1]^[5] By sensing true ambient static pressure, the device corrects position errors in the aircraft's instrumentation, ensuring reliable performance during flight testing and certification processes.^[3] Developed in the mid-20th century to address the limitations of traditional static ports on high-performance aircraft, the trailing cone emerged as a solution to the inaccuracies caused by shock waves and boundary layer influences on airframe-mounted sensors.^[3] Early concepts originated from work by the Royal Aeronautical Society in the 1950s, with refinements by companies like Douglas Aircraft and the Federal Aviation Administration (FAA) through the 1960s, driven by the need for better altimeter accuracy across subsonic to supersonic speeds.^[3]^[1] In basic operation, the cone trails 1-2 fuselage lengths behind the aircraft to escape its aerodynamic influence, with static pressure ports positioned forward of the cone to capture freestream conditions without interference.^[5] This positioning allows the ports to align naturally with the undisturbed airflow, stabilized by the cone's drag, thereby providing a direct measure of ambient static pressure for comparison against the aircraft's onboard systems.^[1]^[3]

Underlying Principles

The trailing cone operates on the aerodynamic principle that positioning the measurement device sufficiently far aft of the aircraft—typically 30 to 60 meters behind—places it outside the viscous wake and distorted pressure field generated by the fuselage, wings, and other structures, enabling the static pressure ports on the cone to sample near-true freestream conditions.^[6] This distance, often equivalent to one or two wingspans, ensures the cone resides in a region where the airflow has recovered to ambient static pressure, free from local accelerations or decelerations induced by the aircraft.^[7] The underlying fluid dynamics rely on Bernoulli's principle, which relates static pressure to airspeed and altitude through the equation p_s + \frac{1}{2} \rho V^2 = p_t, where p_s is static pressure, \rho is air density, V is true airspeed, and p_t is total (stagnation) pressure; the trailing cone corrects for position errors in aircraft static ports by providing a reference p_s that minimizes deviations from this ideal relationship.^[7] The cone's streamlined shape, such as an ogive or pointed nose with a flared base, reduces its own aerodynamic drag while allowing tension in the connecting tube to maintain a stable trailing angle, ensuring consistent alignment with the local flow.^[6] Stabilization of the trailing cone is achieved through its geometry, which generates a restoring aerodynamic moment that self-aligns the device with the freestream direction, thereby preventing oscillations or misalignment due to turbulence or sideslip.^[8] This passive mechanism, combined with the drag from the cone's perforated or finned design, keeps the tube taut and the system steady during level flight, though it is limited to quasi-steady conditions to avoid dynamic instabilities.^[6] The primary benefit is the reduction of position error \Delta p_{pos} = p_{s,a} - p_s, where p_{s,a} is the aircraft static port pressure and p_s is freestream static pressure; this error can reach several percent of dynamic pressure q = \frac{1}{2} \rho V^2 in transonic flows due to shock-induced distortions, but the trailing cone typically limits it to 0.1–0.2% of q in well-calibrated subsonic setups.^[7]^[8] The correction for true static pressure using trailing cone data is derived from pressure coefficient differences. The measured pressure at the cone is p_c = p_s + C_{p,c} q, where C_{p,c} is the cone's pressure coefficient (often near zero due to its freestream placement). Similarly, the aircraft port pressure is p_{s,a} = p_s + C_{p,a} q, with C_{p,a} capturing the position error coefficient. Rearranging yields the true freestream static pressure approximation:

p_s \approx p_c + \frac{1}{2} \rho V^2 (C_{p,c} - C_{p,a})

This equation accounts for any residual C_{p,c} (calibrated separately) and the known or estimated C_{p,a}, providing a direct link between cone and airframe measurements; in practice, C_{p,c} is minimized by port placement on the cone's cylindrical section.^[7] For subsonic cases, such as at sea level with Mach 0.3, this yields altitude accuracies of ±8 feet (corresponding to ~0.3 hPa pressure error), while at 60,000 feet, errors remain below ±37 feet.^[7] In transonic regimes up to Mach 0.9, normalized errors \Delta p / [q](/page/Q) are around -0.0026 at Mach 0.8, though calibration complexity increases due to compressibility effects, limiting overall accuracy to ~0.2% of [q](/page/Q) without additional wind-tunnel validation.^[7]

Design and Components

Cone Structure

The trailing cone is typically constructed as a lightweight, streamlined cone-shaped body designed to minimize aerodynamic disturbance while ensuring stable trailing in freestream conditions. Representative designs feature a base diameter of 5 to 10 inches (12.7 to 25.4 cm) and an apex angle of 32 to 42 degrees, enabling reliable alignment and stability at angles of attack up to 10 degrees during flight testing.^[1]^[9] The cone length varies by application but is generally 20 to 80 cm to accommodate internal pressure sensing components while maintaining a low-drag profile.^[5]^[1] Static pressure ports are integrated as multiple flush-mounted orifices along the cone's internal pressure tube or surface, typically numbering 4 to 48 in arrays (e.g., four rings of 12 orifices each, spaced 30 degrees apart azimuthally and positioned 4 to 10 cone diameters forward of the apex). These ports connect to an internal manifold or averaging chamber to mitigate asymmetries and provide accurate freestream static pressure measurement.^[1] The cone body is fabricated from high-strength, low-weight composites such as epoxy-resin fiberglass or composite fibers to balance durability and minimal mass, while corrosion-resistant alloys like stainless steel are used for ports, fittings, and structural reinforcements to endure environmental exposure during deployment.^[1]^[10] Total mass is maintained below 5 kg (e.g., 1.25 kg for compact models) to reduce tube tension needs and aircraft drag increment, which remains negligible at under 0.1% of total drag in operational use.^[10]^[9] Manufacturing adheres to aerospace standards, including surface finishes of ±0.1 mm or better to promote laminar flow over the ports and ensure measurement precision, with components produced by certified facilities compliant with AS9100 for FAA and EASA-approved RVSM applications.^[10]^[11]

Tubing and Deployment Mechanism

The tubing in a trailing cone system consists of a high-strength, flexible hose designed to transmit static pressure signals while supporting the mechanical load of trailing the cone behind the aircraft. Typically constructed from nylon-reinforced materials such as Nylaflow® with embedded steel cable for tensile strength, the tubing has a diameter of 6-10 mm and lengths ranging from 50 to 100 meters to ensure the cone trails sufficiently far (often 1.5 to 2 fuselage lengths) from the aircraft's disturbed airflow.^[12]^[1]^[10] These specifications allow the tubing to withstand tensions up to 500 N and internal pressures suitable for pneumatic transmission, with maximum loads around 534 N and leak-tested at 10-12 psi to maintain signal integrity.^[10]^[5] Deployment hardware is mounted in the aircraft's tail or fuselage section for optimal positioning and includes a motorized reel system to control the payout and retrieval of the tubing. The reel, often powered by a DC motor with torque control, enables smooth extension during flight without excessive drag or oscillation.^[5]^[3] A fairlead mechanism, typically incorporating stainless steel skids or bushings, guides the tubing to prevent chafing against the aircraft structure during operation.^[1]^[12] The tubing provides an internal pathway for transmitting static pressure signals from ports on the cone to the aircraft's instrumentation, minimizing errors from airflow disturbances. Multiple orifices on the cone feed into an averaging chamber within the tubing, which connects via small-diameter lines (e.g., 0.04-0.135 inches) to transducers like Paroscientific models with 0.01% accuracy.^[1]^[5] To isolate vibrations and pressure lags, systems often incorporate flexible manifolds or bladders, with corrections applied for dynamic errors on the order of ±0.2 mb during stabilized flight.^[4] Safety features include breakaway links or shear pins integrated into the reel assembly to allow jettisoning the cone in emergencies, preventing entanglement or structural damage.^[3] Tension sensors monitor deployment stability, alerting to excessive loads (e.g., from cone deformation at dynamic pressures above 10 in Hg), while protective sleeves like Kevlar® cover the initial tubing segment to resist heat and abrasion up to 250°F.^[12]^[10] Integration with standard aircraft pitot-static systems is achieved through AN fittings and adapters, enabling direct connection to altimeters or data logging equipment such as PC/104 systems for real-time recording.^[10]^[12] This compatibility supports applications like RVSM certification, with optional wireless links for remote data acquisition up to 950 ft.^[5]

Operation and Calibration

Deployment Procedure

The deployment procedure for a trailing cone system begins with thorough pre-flight preparations to ensure system integrity and operational safety. Operators inspect the cone, tubing, and any associated reel or winch mechanism for damage, such as cracks, abrasions, or wear that could compromise structural integrity during flight. Pressure lines are calibrated on the ground using standards traceable to national bureaus, with leak tests conducted under simulated altitude conditions (e.g., 20,000 ft equivalent) to verify rates below 100 ft/min, typically achieving 40-60 ft/min. Clear airspace behind the aircraft is confirmed, and instrumentation like transducers is verified for accuracy within recent calibration windows, often 60 days for critical systems.^[12]^[13]^[4] In-flight deployment is initiated once the aircraft reaches a low speed, typically below 110 knots calibrated airspeed (KCAS), to minimize initial aerodynamic loads. For systems equipped with an onboard winch or reel, the tubing is gradually paid out from the cockpit or via ground control linkage, allowing the cone to extend 15-24 meters behind the fuselage in level flight at constant speed and altitude (e.g., Mach 0.4 at 3,000 meters). Tension in the tubing is monitored to ensure stability, with the cone achieving full extension and pressure stabilization as speed increases to 200-300 knots true airspeed, where it trails at least one fuselage length in undisturbed airflow. Ground-deployed systems, such as those mounted on the vertical stabilizer, may extend the cone at a 45-degree angle prior to takeoff, with the cone "flying" naturally during rollout and stabilizing in cruise.^[12]^[4]^[5] During operation, continuous monitoring is essential to maintain cone stability. Oscillations are checked using tension sensors, accelerometers, and visual observation from chase aircraft, limiting angular deviations to under 30 degrees to prevent dynamic errors in pressure readings. Flight speed is adjusted to sustain a stable trail, with data recorded only after stabilization (e.g., 1-3 minutes in level legs), avoiding periods of non-steady conditions that could introduce lags of several seconds in the system. In-flight photography or telemetry confirms the cone's position relative to the aircraft wake, ensuring it remains in free-stream air.^[12]^[4]^[13] Retraction follows a controlled sequence to avoid damage from whipping or entanglement. The aircraft slows to below 150 knots, and the tubing is reeled in at a steady rate using the winch mechanism, with stability issues noted during the final 7-10 meters of recovery. Upon landing, the pilot executes a sharp turn to clear the exhaust plume, allowing ground crew to coil the tubing and secure the cone (e.g., to a missile rail or stowage point) using ties or clips. A post-flight inspection examines the entire system for deformation, heat damage, or wear, replacing components if necessary.^[12]^[4]^[5] Safety protocols prioritize abort criteria and emergency measures throughout the procedure. Deployment or flight is aborted if excessive drag is detected (e.g., via thrust increases exceeding operational norms) or structural warnings appear, such as tubing anomalies or cone instability beyond safe limits. Systems incorporate quick-release or jettison mechanisms for emergencies, tested over unpopulated areas, and all operations adhere to clean aircraft configurations with retracted gear and flaps at speeds above 70 m/s. Coordination with chase aircraft and ground teams ensures real-time feedback, with reinforced tubing (e.g., Kevlar sleeving) protecting against heat and abrasion.^[12]^[13]^[11]

Pressure Measurement Process

The pressure from the static ports on the trailing cone, typically consisting of multiple orifices arranged in rings to average the freestream static pressure, is transmitted pneumatically through a flexible tubing system—often nylon or similar material with an inner diameter of about 0.635 cm—to onboard transducers located in the aircraft.^[1] These transducers, such as Rosemount models or Paroscientific DigiQuartz units with accuracies of 0.01% to 0.5% full scale, convert the pressure signal into electrical outputs for data acquisition systems.^[4]^[5] The system samples the pressure data at rates ranging from 10 Hz to 100 Hz, enabling real-time monitoring during flight test maneuvers while capturing dynamic variations in atmospheric conditions.^[14] The core of the calibration process involves comparing the cone-derived static pressure (P_cone) to the aircraft's onboard static port pressure (P_airframe) across a range of altitudes and Mach numbers, typically during stabilized straight-and-level flight legs lasting 1-3 minutes.^[4] The position error, which represents the altitude offset due to inaccuracies in the airframe static ports, is computed using the formula:

\Delta h = \frac{RT}{g} \ln\left(\frac{P_\text{cone}}{P_\text{airframe}}\right)

where R is the gas constant for dry air (287 J/kg·K), T is the ambient temperature in Kelvin, and g is gravitational acceleration (9.81 m/s²).^[1]^[4] This equation derives from the hydrostatic relation in the atmosphere, where the pressure lapse rate is dP/P = -(g / RT) dh; integrating assuming isothermal conditions yields the logarithmic form, with the sign convention indicating that P_cone approximates freestream pressure more accurately than P_airframe, which may be perturbed by local flow effects.^[1] For example, at a true altitude of 10,000 m where T ≈ 223 K, P ≈ 265 hPa, and P_cone exceeds P_airframe by 0.5 mb (50 Pa), the resulting Δh ≈ 12 m, providing a correction to indicated altitude and airspeed that scales with flight conditions.^[4] The acquired pressure data feeds directly into the aircraft's flight test instrumentation, such as data acquisition systems (DAS) connected to onboard computers, where it is processed to generate calibration tables mapping indicated airspeed and altitude errors as functions of Mach number and configuration.^[5] To account for tube lag—typically less than 1 second in short-tube setups but up to several seconds in longer configurations—digital filtering or time-lag corrections are applied during real-time processing and post-flight analysis.^[4]^[6] Accuracy is validated post-flight by cross-referencing the calibrated pressures against independent references like GPS-derived true airspeed from D-value maneuvers, yielding static pressure errors as low as ±0.16 mb at 12 km altitude, which translates to indicated airspeed errors below 0.5%.^[4] In wind-tunnel validations, trailing cone systems have demonstrated pressure measurement errors under 0.063% of static pressure, corresponding to Mach number discrepancies less than 0.0006.^[1] Modern enhancements include integrating digital pressure sensors directly on the cone, such as high-accuracy piezoelectric or quartz transducers, paired with wireless telemetry systems operating at frequencies like 915 MHz to transmit data up to 950 ft without pneumatic tubing, thereby eliminating lag and enabling higher-fidelity measurements in dynamic flight regimes.^[5]

Applications and Usage

Flight Testing

Trailing cones play a critical role in aircraft flight testing by providing a reference for calibrating static pressure sources in air data systems, particularly during high-speed runs that expand the performance envelope of new designs. This calibration ensures precise measurements of airspeed and altitude, which are essential for validating stall speeds and Mach number limits. By trailing behind the aircraft at a distance of at least one fuselage length, the cone minimizes position errors caused by the aircraft's aerodynamic interference, allowing for accurate determination of free-stream static pressure.^[11]^[4] Flight test scenarios involving trailing cones typically encompass subsonic to transonic regimes, with Mach numbers ranging from 0.3 to 0.95, conducted in straight-and-level unaccelerated flight at altitudes between 4,500 and 12,500 meters. Maneuvers are performed to map position errors, including variations in angle of attack limited to small values (less than 2 degrees) to maintain cone stability, though broader ranges such as -5 to +15 degrees may be indirectly assessed through complementary data. These tests occur in clean configurations at speeds above 70 m/s, often using pacer aircraft for verification via overtake maneuvers. Historical applications include later tests on the NCAR Sabreliner in the 1980s for pressure survey missions.^[1]^[4]^[3] The primary data output from trailing cone tests consists of correction curves plotting position error against dynamic pressure, which are applied to pitot-static computers to refine air data computations. These curves achieve high accuracy, reducing static pressure errors to approximately ±0.39 millibars, corresponding to airspeed uncertainties of less than 1 knot in typical conditions. Integration into FAA and EASA certification campaigns involves pre-flight leak checks, deployment at specified trail lengths (15-18 meters), and multiple short flight legs (1-3 minutes each) totaling several hours per program, often 10-20 flight hours to cover the required matrix for envelope validation.^[4]^[3]^[15]

RVSM Certification

Reduced Vertical Separation Minimum (RVSM) operations are mandated in airspace from flight level 290 (FL290) to FL410, where the vertical separation between aircraft is reduced to 1,000 feet to increase airspace capacity. To ensure safety, aircraft altimetry systems must achieve high precision, including an automatic altitude control system capable of maintaining altitude within ±65 feet at a 95% probability during stabilized flight. Trailing cones play a critical role in calibrating the aircraft's static pressure ports to minimize altimetry system error (ASE), targeting a total ASE below 200 feet to meet these requirements.^[16] The RVSM certification process involves deploying the trailing cone during dedicated flight tests to measure freestream static pressure and verify overall altimetry performance. These flights assess the total ASE across various Mach numbers, weights, and configurations, ensuring it remains under 200 feet. The procedure incorporates temperature compensation to account for environmental variations and hysteresis checks to evaluate pressure recovery differences during acceleration and deceleration, confirming the system's reliability under operational stresses.^[16]^[17] Regulatory standards for RVSM certification are outlined in FAA Advisory Circular 91-85B, which provides guidance on aircraft airworthiness approval, including static system calibration methods like trailing cones. In Europe, equivalent requirements are detailed in Eurocontrol's Guidance Material for RVSM operations, emphasizing height-keeping performance. Data collected from trailing cone deployments informs adjustments to the aircraft's barometric altitude settings and static system error correction (SSEC) tables, enabling regulatory approval for RVSM entry.^[16]^[18] Trailing cone usage is prevalent in certifying business jets, where dedicated flights validate static port accuracy and confirm compliance with ASE limits before obtaining RVSM operational approval. These tests ensure the aircraft meets the stringent height-keeping standards required for high-altitude en route operations, and as of 2025, trailing cone data continues to support RVSM monitoring requirements.^[17]^[19] Typically, RVSM certification via trailing cone involves 5-10 dedicated flights to gather sufficient data points, streamlining the process by delivering precise freestream pressure measurements that reduce reliance on ground simulations. This approach can lower overall certification timelines and costs, often ranging from $70,000 to $100,000 for business jet operators.^[20]^[17]

Advantages and Limitations

Key Benefits

Trailing cone systems provide superior accuracy in measuring freestream static pressure compared to fuselage-mounted ports, achieving errors as low as 0.016% to 0.063% of static pressure across Mach numbers from 0.30 to 0.95, which corresponds to Mach number errors less than 0.0006.^[1] In contrast, fuselage static ports are susceptible to position errors due to the aircraft's aerodynamic disturbance field, often resulting in higher inaccuracies that require extensive corrections.^[6] This precision enables reliable calibration of air data systems, with pressure differences typically ranging from 0.08% to 0.25% of impact pressure and minimal sensitivity to Reynolds number variations.^[1] The versatility of trailing cones allows their use across a broad range of speed regimes, from subsonic (Mach 0.30) to transonic (up to Mach 0.95) and potentially supersonic conditions, without requiring major modifications to the system.^[1]^[6] Unlike fixed-length boom probes, which are constrained by structural limitations and stability issues at higher speeds, trailing cones maintain stability through adjustable tube lengths—often two wingspans or more—ensuring alignment with freestream flow via proper orifice placement 5-6 cone diameters ahead of the tip.^[6] This adaptability supports calibration in various flight envelopes while remaining effective in steady level flight.^[6] Trailing cones offer cost-effectiveness as a reusable calibration tool, serving as a practical alternative to expensive methods like pacer aircraft or radar tracking for large-scale programs.^[6] Their design facilitates quick deployment and economical testing, reducing overall program expenses compared to dedicated calibration infrastructure. Additionally, the systems impose minimal interference on aircraft performance, with total weights around 8.5 pounds (approximately 3.85 kg) and drag forces on the order of 7.7 pounds at moderate speeds, allowing normal flight profiles without significant alterations.^[5]^[1] Developed and tested since the 1950s, trailing cones have demonstrated proven reliability over more than 50 years of operational use in flight testing and certification, supported by extensive validation in wind-tunnel and in-flight studies with consistent stability and low error margins.^[6] Modern implementations, including self-contained variants, have operated reliably for over six hours during extended tests, transmitting data accurately over distances exceeding 950 feet.^[5]

Potential Drawbacks

Trailing cone systems, despite their utility in aircraft static pressure calibration, are subject to several operational challenges and limitations that can impact safety, accuracy, and efficiency. Deployment of the trailing cone carries risks of tubing instability or oscillations, particularly in turbulent airflow, which may lead to data inaccuracies or potential entanglement with the aircraft. These issues necessitate deployment only in calm atmospheric conditions and require experienced pilots to maintain steady, unaccelerated flight to minimize excursions.^[13] An emergency release mechanism is essential to prevent structural damage or control interference in case of malfunction.^[13] The system's effectiveness is constrained by speed and altitude ranges. At low speeds, the cone's weight can cause sagging of the tubing, potentially introducing total pressure errors into static measurements and limiting reliable use below approximately 100 knots, where alternatives like trailing static bombs are preferred for low-speed calibration.^[21] At high speeds, tubing flutter may occur, with the trailing bomb variant unstable above 200 knots, while cones have been tested successfully up to Mach 1.12 but may require specialized designs or alternatives to avoid dynamic instability at higher supersonic speeds.^[13]^[3] Altitude operations are typically restricted below 10,000 feet for optimal performance, with higher altitudes demanding additional position error verification due to varying atmospheric effects.^[13] Maintenance requirements add to operational burdens, as the tubing and cone must undergo pre- and post-flight inspections for wear, leaks, and structural integrity, alongside instrument calibration every 60 days using approved facilities. These demands can elevate costs relative to permanent static ports, though exact increments depend on usage frequency.^[13]^[12] Certification presents hurdles, as trailing cones are classified as temporary test equipment requiring approval under regulations such as 14 CFR § 23.1325, including demonstrations of dynamic balance and structural soundness across the operating envelope. All collected data must maintain traceability for regulatory audits, ensuring compliance with accuracy standards like ±30 feet per 100 knots for static pressure errors.^[13] Environmental sensitivities further complicate use, with the system vulnerable to turbulence-induced oscillations that degrade measurement precision, mitigated by restricting flights to smooth air masses. Potential icing on the cone or tubing in adverse weather can alter pressure readings, often addressed through operational avoidance or protective measures like heated sleeves, while bird strikes pose risks of physical damage to the exposed trailing elements, necessitating vigilant flight planning.^[13]