(ii) HIRF. Perform HIRF testing in accordance with § 27.1317 and the guidance in section
27.1317 of this AC.
(5) Night vision imaging system (NVIS) lighting. If the EDS is designed with night vision goggle (NVG) compatibility for installation in a NVIS lighting modified cockpit, refer to MG-16 of this AC and RTCA Document DO-275, "Night Vision Imaging System Lighting," for lighting performance guidance.
Modifications to EDS displays should preserve color uniformity across the cockpit. Most EDSs incorporate color; as a result, in order to preserve the EDS colors close to the rotorcraft's designed colors, the NVIS lighting system should be modified to be compatible with Class B NVGs. Lighting compatible with Class A NVGs may not provide the correct color hues (e.g., red colors tend to look orange or amber, yellow colors tend to have a green tint in daylight, etc.).
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CHAPTER 3
AIRWORTHINESS STANDARDS
NORMAL CATEGORY ROTORCRAFT
MISCELLANEOUS GUIDANCE (MG) AC 27 MG 20. HUMAN FACTORS (HF)
a. Background. The purpose of this miscellaneous guidance section is to provide applicants with general guidelines on how to approach compliance with 14 CFR part 27 sections that have provision relating to human factors (HF) or human performance. The intent of this guidance is to assist in understanding the HF implications of the more frequently referenced regulations. This guidance also provides examples of how to address HF implications when demonstrating compliance with these regulations. This information should help determine whether HF-related requirements have been adequately addressed.
(1) Developments in technology and the affordability of advanced avionics provide for the installation of sophisticated systems into rotorcraft. As a result, the level and characteristics of pilots' interactions with cockpit and avionics systems is changing, particularly for rotorcraft that are not capable of operating under instrument flight rules (IFR). Additionally, integrating new technologies, such as a satellite-based augmentation system (SBAS) or wide area augmentation system (WAAS) increases the rotorcraft's avionics capabilities to perform functions and operations it was not previously capable of performing. These new capabilities create HF issues related to pilot workload that should be evaluated along with the systems integration. Poor system integration often results in applicants relying on the pilot to work around a design issue. This approach, coupled with complex pilot interfaces, can lead to pilot error and may inhibit the pilot's ability to recover from errors without undue concentration or fatigue.
Some HF implications are straightforward and easily complied with, while others may be more complex.
A partial list of rules that have HF implications, particularly those that relate to pilot workload, is included in paragraph b. (2) below. The HF guidance contained in this MG is consistent with the goals identified in the FAA Industry Guide to Product Certification (Jan 99) and the FAA Industry Guide to Avionics Approvals (Apr 01).
(2) The requirements of part 27 Subparts A through G apply to rotorcraft approved for both VFR and IFR operations. Rotorcraft approved for IFR operations must also meet the requirements of Appendix B to part 27 (Airworthiness Criteria for Helicopter Instrument Flight). Additionally, Appendix D to part 25 contains information regarding criteria for minimum crew determination for airplanes operating under FR conditions, which may be beneficial for determinations in rotorcraft.
(3) As a normal part of the certification project, the applicant and the FAA AUTHORITY usually establish an early and formal written certification plan on the certification basis, the methods of compliance, and the schedules for completing the certification project. Both parties should ensure coverage of the HF aspects of the rules in the plan. If the applicant chooses, it can submit a separate human factors certification plan. These early discussions can reduce the applicant's time and cost to obtain certification.
(4) The flight test team usually performs the HF evaluations. However, HF engineers and test pilots should be involved early in the design, during cockpit integration tests, and early in the humanmachine interface evaluations. Identify and develop pilot-system interfaces and interactions in the basic design to reduce the risk of having an interface issue identified after the system design is final.
b. Related Regulations and Documents.
(1) HF related regulations. Not all of the regulations listed require specific HF means of compliance. Some are self-explanatory and straightforward, while compliance with others is determined during flight test as part of their normal course of testing and evaluation. However, each regulation should be noted in the certification plan.
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AC 27-1B, Chg 7 2/4/2016
(2) Many of the regulations with HF implication are also within the purview of other engineering disciplines; therefore, demonstration of compliance with 14 CFR part 27 may include more than one engineering discipline. For regulations with HF implications, consider identifying which discipline or individual will be responsible for demonstrating compliance with these regulations. The following contains a partial list of part 27 regulations related to human factors and performance.
14 CFR Section Title
27.2(a)(1)-(2) Special retroactive requirements.
27.33(b) (3), (c)(2), (e) Main rotor speed and pitch limits.
27.45(a), (f) General.
27.51(a) Takeoff.
27.75(a), (b) Landing.
27.141(b) General.
27.143(a), (d), (e) Controllability and maneuverability.
27.151(a), (b) Flight controls.
27.161(b) Trim control.
27.171 Stability: general.
27.177 Static directional stability.
27.239 Spray characteristics.
27.251 Vibration.
27.561(a), (b) General.
27.611 Inspection provisions.
Stability augmentation, automatic, and power-
27.672(a), (b), (c)(1)(2) (3) operated systems.
27.679(a), (b) Control system locks.
27.685(d)(10) Control system details.
27.771 (a), (b), (c) Pilot compartment.
27.773(a)(1), (b) Pilot compartment view.
27.777(a), (b) Cockpit controls.
27.779(a), (b) Motion and effect of cockpit controls.
27.783(b) Doors.
27.785 Seats, berths, litters, safety belts, and harnesses.
27.801(a), (b), (d) Ditching.
27.805 (b) Flight crew emergency exits.
27.807 (a), (b), (d) Emergency exits.
27.859(g) (3) Heating systems.
27.863(c) Flammable fluid fire protection.
27.865(b)(1)(2), (c)(3)(5) External loads.
27.901(b)(2)(5) Installation.
27.921 Rotor brake.
27.955(c) Fuel flow.
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14 CFR Section Title 27,995(b) Fuel valves.
27.999(b)(2)(3)(i) Fuel system drains.
27.1141(a), (c), (d) Powerplant controls: general.
27.1143(b), (c), (d) Engine controls.
27.1145(a), (b) Ignition switches.
27.1147 Mixture controls.
27.1151 Rotor brake controls.
27.1189(b)(c) Shutoff means.
27.1301(a), (b) Function and installation.
27.1303 Flight and navigation instruments.
27.1305 Powerplant instruments.
27.1309(a), (b), (c) Equipment, systems, and installations.
27.1321 Arrangement and visibility.
27.1322 Warning, caution, and advisory lights.
27.1329 Automatic pilot system.
27.1335 Flight director systems.
27.1337 (b), (e)(2) Powerplant instruments.
27.1351(d) General.
27.1357(d) Circuit protective devices.
27.1361(a), (c) Master switch.
27.1367(b), (c) Switches.
27.1381 Instrument lights.
27.1383(b), (c) Landing lights.
27.1401(a)(1) Anticollision light system.
27.1411(a), (b)(1) General.
27.1415(b), (d) Ditching equipment.
27.1501(b) General.
27.1523 Minimum flight crew.
27.1525 Kinds of operations.
27.1541(b)(1) General.
27.1543(b) Instrument markings: General.
27.1545 Airspeed indicator.
27.1549 Powerplant instruments.
27.1555 Control markings.
27.1559 Limitations placard.
27.1561 Safety equipment.
27.1583 Operating limitations.
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AC 27-1B, Chg 7 2/4/2016 14 CFR Section Title Appendix B to Part 27, IV Static longitudinal stability.
Appendix B to Part 27, VI Dynamic stability.
Appendix B to Part 27, VIl Stability augmentation system (SAS).
Appendix B to Part 27, VIII Equipment, systems, and installation.
(3) Advisory Circulars (AC) and Related Documents (refer to the current version).
Note: ACS, orders, and policy statement memoranda are available on the FAA website: www.faa.gov.
(i) ACS.
AC Title 20-175 Controls for Flight Deck Systems 21-40 Guide for Obtaining a Supplemental Type Certificate 27-1 Certification of Normal Category Rotorcraft (Sections related to Appendix B and the requirements within Appendix B identified in the certification plan with HF/HP issues) 29-2 Certification of Transport Category Rotorcraft (Sections related to Appendix B and the requirements within Appendix B identified in the certification plan with HF/HP issues) Page MG 20 -4
(ii) Related Documents.
Document Title SAE- ARP 4155 Human Interface Design Methodology for Integrated Display Symbology SAE-ARP 4033 Pilot-System Integration SAE-ARP 4102 Flight Deck Panels, Controls, and Displays SAE-ARP 4102-7 Electronic Displays SAE-ARP 4927 Integration Procedures for the Introduction of New Systems to the Cockpit SAE-ARD 50019 Human Engineering Issues for Enhanced Vision Systems DOT/FAA/RD-93/5 Human Factors for Flight Deck Certification Personnel DOT/FAA/AM-13/21 Multi-Function Displays: A Guide for Human Factors Evaluation
c. Scope.
(1) The objective of this MG is to provide guidance regarding the regulatory HF components that should be considered during a certification project for rotorcraft. While applicants are the main target audience, this guidance can be used by all FAA project team members including:
(i) Aircraft Evaluation Group (AEG) inspectors,
(ii) avionics engineers, (ilI) project managers,
(iv) flight test pilots and engineers,
(v) HF specialists and engineers,
(vi) propulsion engineers, and
(vii) systems engineers.
(2) This MG is general and high level, covering the HF aspects of certificating a rotorcraft or system installation on a new or previously-certificated normal category rotorcraft. It is intended to guide applicants and certification engineers on what they should consider regarding HF during project planning and execution Page MG 20 - 5
AC 27-1B, Chg 7 2/4/2016
d. System Description.
(1) General. Develop a system description with enough detail to provide for a common understanding of the design, function, and operation of the system. Thoroughly detail any new or novel features, interfaces, controls, or other pilot-system interfaces that pilots will use.
(2) Intended function (§ 27.1301).
(i) Describe the intended function of the major pilot-system interfaces. In order to assess the potential hazards posed by the installation of a system, there must be a clear understanding of the function provided by the system and the declared intended function. Accomplish this by providing a detailed description of how the system supports the specified function(s). For example, describing a function or component, such as a display, as "for pilot situation awareness only" or "for situational awareness only" is not adequate regardless of whether the function or component is required by the regulations. A better example for a non-required function might be "to increase terrain awareness."
Identify the following items, as appropriate, focusing on new or unique features that affect the crew interface or the allocation of tasks between the pilot and the rotorcraft systems:
(A) The intended function of the system from the pilot's perspective (coupling between the pilot and the system).
(B) The role of the pilot relative to the system.
(C) The degree of integration or independence with other flight deck equipment.
(D) The novelty of the system or features of the system.
(E) The criticality of the system and alerting mechanism.
(F) Methods to reduce the occurrence and consequences of crew error when interacting with the system.
(G) The system features accessible to the pilot other than those normally considered needed for flight. For example, whether field loadable software, maintenance, and configuration functions are accessible by the pilot in flight and on the ground, or whether they are accessible only by maintenance personnel.
(ii) Use the following information to evaluate whether the intended functions and associated tasks are sufficiently detailed and specific:
(A) Whether each feature includes a statement of the intended function and a description of the task associated with this feature.
(B) Whether there are assessments, decisions, or actions required by the pilot for these intended functions.
(C) Whether other information is to be used in conjunction with these intended functions (for example, other cockpit systems), in combination with the system.
(D) Whether the operational environment in which these intended functions are to be used is adequately described (e.g., VFR, IFR, phase of flight).
(3) Cockpit layout (§§ 27.771, 27.773, 27.777, 27.1303, 27.1305, 27.1321, 27.1329, and Appendix B to part 27).
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(i) Drawings of the cockpit layout showing positions of system components, even if preliminary, are beneficial for providing an understanding of the intended overall cockpit arrangement (controls, displays, sample display screens, seating, stowage, and so forth). Including measurements and dimensions of displays, their locations and locations of controls relative to the pilot's central line of vision or the design eye position is also beneficial to both the applicant's and certification authority teams.
As the system design changes, keep the certification team updated so they are current on proposed changes. Give special attention to the following, especially if they are novel or unique:
(A) Arrangements of the controls, displays, or other cockpit or flight deck features or equipment.
(B) Controls, such as cursor control devices, touchscreen displays, or new applications of existing control technology.
(C) Content, format, and function of the pilot interface on the display as generated by the systems software.
(D) Display hardware technology.
(E) Screen usage, alerting mechanisms, and mode annunciation.
(ii) Sketches of the crew interfaces for the specific systems or the items listed above can be helpful in providing an early understanding of the features that may face certification issues.
(4) Underlying principles for automation logic (§ 27.1309, § 27.1329, and Appendix B to part 21).
Define the system's automated functions design early in the process. The automation features should follow a design philosophy that supports the intended functions regarding the system behavior, modes of operation, and pilot interface with controls, displays, and alerts. For designs that involve significant automation, the way automation operates and communicates that operation to the pilot can have significant effects on the crew interface. The system description should include, but not be limited to:
(i) Pilot actions to engage or disengage, or activate or deactivate, modes and features.
(ii) Principles underlying mode transition.
(iii) Mode annunciation scheme.
(iv) Automation engagement or disengagement principles.
(v) Level of automation.
(vi) Logic diagrams and complexity of the logic, if available.
(vii) Failure modes, how they appear to the pilot, and how the pilot's interaction with the system and rotorcraft changes.
(5) Operational considerations (§ 27.1523, Minimum flight crew; § 27.1525, Kinds of operations).
Consider consulting the AEG inspector that is responsible for the make and model of rotorcraft on the system installation.
(1) Pilot characteristics (§ 27.1523). The FAA has not accepted certain designs, in past projects, that specifically relied on crew resource management or certain pilot characteristics to mitigate a system design flaw. Consider assessing the level of certification, skill, and knowledge a "nominal pilot" possesses in order to evaluate the pilot workload when interacting with the system and rotorcraft.
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AC 27-1B, Chg 7 2/4/2016
(ii) Identify the operations the system is designed to support. Although sometimes considered less complex than installations for operation under IFR, the HF evaluation of installations for operation under VFR should include the same rigor, as both present HF challenges to the pilot. For example, complex systems or systems that require the pilot to spend considerable time interfacing with a system's functions and interactions with other rotorcraft systems will require the pilot to allocate attention from flying the rotorcraft. The results are increased workload with varying changes in the pilot's ability to attend to flying the rotorcraft. The following are some considerations:
(A) For rotorcraft operating only under VFR, describe the operations the system is meant to support, taking into account day and night operations. For example, for installation of an electronic display systems (EDS) display suite that integrates with external GPS navigators, consider:
(1) The effect of the pilot-system interface on the pilot's attention allocation and workload.
(2) How it affects the pilot's external scan and "see and avoid" tasks (whether it requires extensive heads-down time).
(B) For rotorcraft certificated to operate under IFR, describe the operations the system supports. For example, for installation of a new EDS suite and a WAAS GPS system that interfaces with the existing autopilot and one of the new operations is steep angle low speed approaches, consider how the system will support or change pilot workload.
(iii) System Operation procedures. Describe and evaluate the pilot procedures for both normal and abnormal conditions since the design of the system and use of procedures are interrelated.
Additionally, development and presentation of procedures and limitations can affect pilot workload, particularly in abnormal conditions. Identify and evaluate any expected pilot memory or "bold-face" items (procedures that the pilot must perform from memory prior to referencing a checklist or flight manual). In addition to the flight manual or flight manual supplement, system operations procedures may include:
(A) Quick reference handbook to accompany the flight manual.
(B) Abbreviated checklists to accompany the flight manual.
e. Certification Requirements. Identify the regulations in the certification basis for system or component installations that have HF implications. These can be identified either as part of the certification plan or a separate human factors certification plan. The certification plan should indicate the method of compliance for each regulation and contain sufficient detail to ensure human factors considerations are adequately addressed. The plan should also allow adequate time to accomplish all necessary testing agreed to by the applicant and the FAA.
(1) Address and evaluate the following in the certification plan:
(i) The intended use of the system does not require any exceptional skill or generate any unreasonable workload for the pilot.
(Il) The use of the display does not require unreasonable training requirements to demonstrate adequately that the pilot can understand and properly operate the system in all operational environments.
(ili) Demonstration of the design characteristics of the display system support error avoidance and management (e.g., detection, recovery, etc.).
(iv) The display system integration is consistent or compatible with other cockpit controls and creates no added burden on the pilot with respect to the new display system or operation of other Page MG 20 -8
(v) If a failure occurs, it will not prevent the pilot from safely operating the rotorcraft.
(2) The manufacturers should provide design rationale for their decisions regarding new or unique features in a display. Evaluation pilots should verify that the data support a conclusion that any new or unique features have no unsafe or misleading design characteristics.
(3) Several pilots as well as human factors representatives should conduct display and system interface evaluations particularly when the applicant is installing a system for the first time in a particular category of helicopter. More than one test pilot should be used to ensure multiple data inputs. For systems that contain new or unique features, consider a greater number of evaluators. A reasonable amount of training time should be allowed to learn all required features of the display system. The evaluators should be familiar with the guidance contained in this advisory circular before performing the evaluation. Additional information helpful in developing evaluation plans. For instance, example information regarding evaluation plan development can be found in GAMA Publication No. 10, Recommended Practices and Guidelines for Part 23 Cockpit/Flight Deck Design; DOT/FAA/AM-01/17, Human Factors Design Guidelines for Multifunction Displays; and section AC 27 MG 19 of this AC.
f. Methods of Compliance. The parts of the certification plan that address the HF portions of the regulations should describe the methods used to demonstrate compliance with sufficient detail to allow the certification authority to evaluate the appropriateness and adequacy of the proposed methods of compliance. It is important that the proposed methods of HF compliance are coordinated and discussed with the certification authority to identify HF issues early in the program to avoid certification schedule delays. Paragraph h. of this MG below, contains a sample compliance matrix for HF.
g. Discussion of selected part 27 regulations related to human factors and performance.
(1) For the purposes of brevity, the regulations discussed are not restated. For all compliancerelated documents, the certification plan should use the exact wording of the regulation.
(i) This part of the guidance does not include all regulations associated with HF and flightcrew interfaces listed in the table in paragraph b. above. In addition, several of the regulations are written in general terms. In these cases, subjective data are often used to establish compliance
(il) Due to the subjective nature of many of the HF aspects of the regulations, the certification authorities encourage applicants to carefully consider and thoroughly describe the means they intend to use to demonstrate compliance with each regulation. The applicant may choose to provide the detailed description of the means of compliance in subsequent submitted test plans. Use the information contained in the discussion for each regulation, presented paragraph g. (2), to assess the appropriateness and adequacy of the chosen methods. The certification authority and the applicant should meet to discuss and reach agreement as to the acceptability of the proposed techniques prior to the collection of compliance demonstration data. Demonstrate compliance through similarity and minimal testing for simple and straightforward applications that have little impact on pilot workload, system awareness, tasking, or performance. It should be understood that the regulations discussed in paragraph g. (2) are (Ili) More complex, integrated designs may require pilot evaluation under actual anticipated flight conditions after the performance of analytical and component-level bench evaluations. For these tests, it is critical the flight test pilots are objective regarding their performance using systems and controls. If using pilots other than test pilots, observers should be alert to possible differences between how the pilot performs and interfaces with a system and the pilot's ratings. The test program should include sufficient simulation and flight testing to ensure:
(A) Reasonable training times and learning curves.
(B) Acceptable interpretation and operation error rates equivalent to or less than previously certificated comparable systems.
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AC 27-1B, Chg 7 2/4/2016 (C) The intended user (pilot) of the system does not require any exceptional skill, strength, or alertness to operate the system.
(D) Proper integration and compatibility with other controls or displays, or both, and with other equipment in the cockpit.
(iv) Typically, rotorcraft systems are designed to minimize failures. However, if a system failure occurs, the pilot should be able to continue safe operation of the rotorcraft. Pay particular attention to the hazards of presenting misleading information to the pilot in the event of malfunction. Applicants are encouraged to conduct early analyses and evaluations of new systems to facilitate timely identification and resolution of HF related certification issues.
(2) The following is a partial listing of the HF-related regulations and associated discussion of each of those regulations with considerations for demonstration of compliance.
(i) Section 27.672.
(A) Section 27.672(a). Provide a warning signal that is distinguishable from other cockpit alerts. If an audio signal is used, the pilot must be able to discriminate it from all other cockpit audio alerts.
(1) Conduct evaluations in the rotorcraft during both ground and flight operations with varying levels of background noise.
(2) Assess the discriminability of the visual and auditory alert in multiple alert scenarios, if applicable.
3) Applications that employ voice technology should meet these same criteria.
(4) Conduct analysis, simulation, or flight test to show that the system would not produce nuisance alerts when the rotorcraft is conducting normal flight operations.
(B) Section 27.672(b). Determination of exceptional pilot skill or strength is subjective.
When evaluating for "exceptional pilot skill," evaluators should consider the complexity of the task in terms of the performance requirement (level of accuracy or precision), the number of steps, memory load, checklist use, time-to-perform, and, if needed, training requirements. The test pilots involved in the program normally do these evaluations. For "exceptional pilot strength," it is also important to conduct evaluations considering the minimum strength capabilities of the pilot. Consider using pilots that represent a fifth percentile female as the low-end of the strength spectrum.
(1) There is guidance that may be useful to applicants in determining strength considerations in section 27.143 of this AC and the strength study in Human Force Exertions in Aircraft Control Locations, report no. AMRL-TR-71-119, February 1972. This study provides several examples of maximum force exertion from various locations of controls in the cockpit; however, there are always unique situations that can arise during the design of a new or modified cockpit.
(2) When new or unique situations arise, conduct evaluations early on to ensure that the strength required to activate the control does not fall outside the limitations of the pilot population.
(ii) Section 27.679. A number of accidents have occurred because pilots have tried to take off with either the manufacturer's control lock or a substitute device in place. A couple of issues can cause this problem. One is whether the "unmistakable warning to the pilot" is, in fact, unmistakable.
Another is the use of unapproved devices to lock the control system. Various approaches and devices have been developed to make it apparent that the control is locked. When evaluating a control lock system, consider several factors in finding compliance with the regulation.
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(A) The lock and its warning, if separate from the lock, should be easily discernable during both day and night operations. Consider the color, location, shape, and accessibility of the device, ease of removal by a seated pilot, and legibility of any placards, etc.
(B) The system operation should be obvious. It should only be possible to install the lock such that the warning placard is properly displayed.
(C) When engaged, the lock design should limit the operation of the rotorcraft so that the pilot receives unmistakable warning in the cockpit before takeoff by an effective means such as:
(1) preventing the application of sufficient engine power to attempt takeoff,
(2) preventing or changing a method of grasping or holding a primary control such as the cyclic or collective, or
(3) use of an audio warning device that cannot be disengaged.
(D) For rotorcraft with separate locks for collective and cyclic, where one lock is removable independently of the other, each lock should independently meet these criteria.
(iii) Section 27.771. This regulation correlates with most of the other HF-related regulations, particularly in situations where a pilot may allocate attention to a particular system or task at the expense of flying the rotorcraft. Applicants should identify aspects of the pilot-rotorcraft interface that might require significant or sustained concentration or physical effort which can lead to distraction and fatigue. Many factors can affect concentration and fatigue, such as noise, vibration, seat comfort, excessive control forces, and poorly designed displays, controls, or pilot-system interfaces. Methods of compliance should focus on evaluation procedures that examine potential concentration demands and sources of fatigue for the flightcrew. Some issues that can contribute to unreasonable concentration or fatigue are:
(A) Pilot-system interface. Interface design can potentially result in a large concentration trap. Interfaces that require substantial heads-down time in rotorcraft without stability augmentation systems can lead to the rotorcraft deviating from the pilot's intended flight path. The system's ability to support the pilot regarding input, cross-check, error identification, and recovery contributes to the attention resources the pilot uses and resulting concentration. Evaluations on a bench or simulator where the system interface is accurately portrayed can help identify potential issues. Flight evaluation will also provide valuable information regarding the design and pilot's ability to work with that design.
(B) Display design. A number of factors associated with display design can ultimately affect concentration and fatigue. Displays that are difficult to read or contain poorly organized information, or lack necessary information, result in greater demands on pilot attention and concentration.
Conduct evaluations under operationally representative scenarios to assess the effectiveness and (C) Cockpit and system control design and function. The ease of identification, accessibility, and usability of cockpit controls can affect the level of pilot concentration. Conduct evaluations to ensure all cockpit controls are easy to identify, access, and operate as required in flight.
New control interfaces, such as touch pads or voice-command, should be evaluated in as many operational environments as possible to assess the pilot's ability to perform tasks requiring their use.
(D) Pilot seats. Poorly designed seats have the potential to create fatigue. Evaluate seats to determine if they contribute a significant amount of fatigue. Conduct these assessments using test participants and gathering subjective data. Conduct assessments based upon the expected average length of flight time the pilot remains in the seat, for a typical flight for the rotorcraft under evaluation.
Subjective comments should be solicited from test participants concerning muscle tension, "hotspots" (areas where harder body contact is experienced), and body soreness or discomfort. Lateral support in the seat pan and lumbar support in the seat back have been used to increase seat comfort.
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