AC 29-2C, Chg 7 2/4/2016
(i) RTCA Document DO-178CB, Software Considerations in Airborne Systems and Equipment Certification, dated December 13, 2011.
(ii) RTCA Document DO-254, Design Assurance Guidance for Airborne Electronic Hardware, dated April 19, 2000.
(iii) RTCA Document DO-297, Integrated Modular Avionics (IMA) Development Guidance and Certification Considerations, dated November 8, 2005.
c. Background. The FAA recognizes the importance of timely completion of an FHA to minimize TC, amended TC, STC, amended STC, and TSOA project delays and potential risks of redesigns required late in a project because of information obtained from the completed FHA. Applicants are expected to not only properly complete FHAs as early as possible to minimize the risks described above, but also obtain FAA acceptance of the FHAs.
d. When to create an FHA. The FAA expects a discussion of the FHA take place during the very early stages of the TC, amended TC, STC, amended STC project (i.e., during the Familiarization Briefing). This will provide the FAA with the necessary design safety aspects information while the development is still in the conceptual and requirements definition phases. Since the FHA process is designed to provide the system level safety and derived requirements, it is imperative that the applicant obtain FAA acceptance of the FHA as early as possible in the systems development (i.e., prior to submitting the certification plan). This will minimize the risk of the applicant’s design requiring changes late in the program to satisfy safety requirements obtained from the completed FHA.
e. How to create an FHA.
(1) The process to create an FHA can be considered fairly complicated if doing it for the first time. T his guidance presumes that an applicant is familiar with ARP 4761 and is looking for some additional guidance in recognizing some of the likely functions of each system and the associated failure conditions (FC) that should be reflected in a FHA. The table in Figure AC 29 MG 21- 1 provides a snapshot of considerations an applicant should address when examining their design for a systematic safety review.
This table is not a complete list nor are the FCs listed in the figure applicable for all designs.
(2) One additional item is the need to include a complete list of assumptions made when developing the FHA. These assumptions may include the intended aircraft (single or dual engine, existing certificated interfacing equipment), type of operation
(e.g., IFR, VFR, category A), crew composition (e.g., single pilot, dual pilot), etc. These should be listed in the front of the document prior to the functional failure conditions matrix.
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(3) The set of tables in Figure AC 29 MG 21-1 provides examples of a format for the system level FHA as identified in the reference ARPs. Guidance is also included for typical entries for the columns with a short description of each as follows:
(i) ATA. This column was taken from the “Joint Aircraft System/Component (JASC) Code Table” document to provide a complete list of systems defined on an aircraft. It is not a typical column entry for an FHA and should not be considered as such. However, it provides systematic approach to identify various aircraft systems.
(ii) Function Description. A concise description of the sub-functions for each top level system. For example, the oil system is made up of sub-functions such as oil pressure, oil temperature, and oil quantity.
(iii) Failure Condition (FC). A goal of this guidance is to encourage the author of an FHA to use the verbiage established in this guidance as a means to provide some standardization and minimize confusion when reviewing FHAs. Typical entries in this column include “Loss of …”, “Unannunciated loss of …”, “Misleading data to the flight crew …”, “Malfunction of …”, along with environmental conditions (e.g., day and night VFR, IFR, Icing).
(iv) Phase of Operation. In this column, the typical entries are Hover, Takeoff, Climb, Cruise, Descent, Approach/Landing, or any combination as appropriate.
(v) Effect of the Failure on the Aircraft, Crew and Occupants. Describe the effects of the failure on the aircraft, aircraft system, flightcrew workload, and occupant safety and comfort. The inclusion of mitigating design features within this column entry is not appropriate and should not be included. Instead, any mitigation required to meet the failure classification should be included in the System Safety Assessment. Each type of effect, not only the effect on flight crew workload, should be analyzed. The effect on the degradation of the system should not be overlooked, as this can result in a higher classification.
(vi) Classification of the FC. This is typically the most challenging entry in the process since it is completely qualitative and requires input from multiple subject matter experts. It requires the participation of various disciplines such as safety analysts, design engineers, engineers responsible for software or complex hardware, human factors specialists, and flight test personnel. After the applicant has determined the classification levels, the results must have concurrence from the certification authority.
This may require lengthy discussions and should occur very early in the certification process.
(A) Some appropriate entries are no effect (NE), minor (MIN), major (MAJ), hazardous (HAZ) or catastrophic (CAT). The definition for each can be found in section 29.1309 of this AC. Note that this column in Figure AC 29 MG 21-1 was intentionally left blank because of the variation of appropriate classifications for a similar failure condition.
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AC 29-2C, Chg 7 2/4/2016
(vii) Supporting Material. For those failure conditions whose aircraft behavior effects are not well defined, additional supporting material (e.g., simulation, studies, flight test) should be defined to validate the chosen classification.
(viii) Verification Method. For each failure condition, the applicant should determine how the aircraft or system design would satisfy the safety objective. Some example entries are provided in Figure AC 29 MG 21-1 such as detailed documents or report numbers used in the supporting material section.
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ATA 22-00-00 – AUTO FLIGHT SYSTEM ATA Function Description Failure Condition (FC) Phase of Operation Effect of the Failure on the Aircraft, Crew and Occupants Classification of the FC Notes (assumptions) Supporting Material Verification Method 2211 Autopilot Computer Loss of autopilot. ALL The detection of the loss of system by the crew could be delayed long enough to significantly reduce the safety margins or functional capabilities.
Analysis and Flt Test Malfunction (hardover) in a single axis.
Hover, TO App/Lnd Aircraft responds with a rapid attitude change, resulting in a possible departure from stable flight, or impact with terrain or ground-based obstacles.
Substantial increase in aircrew workload to recover from the resulting unusual attitude.
Minimal effect on occupants as they will be required to be seated and belted during this phase of operation.
Analysis and Flt Test Figure AC 29 MG 21-1. Generic Examples by ATA.
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AC 29-2C, Chg 7 2/4/2016 Note: Not all ATA chapters or subchapters have been included. Also, the italicized entries are not usually included in the failure condition description but in the systems description or assumptions section.
ATA 22-00-00 – AUTO FLIGHT SYSTEM ATA Function Description Failure Condition (FC) Phase of Operation Effect of the Failure on the Aircraft, Crew and Occupants Classification of the FC Notes (assumptions) Supporting Material Verification Method Malfunction (hardover) in a single axis.
Cruise Aircraft responds with a rapid attitude change, resulting in a possible departure from stable flight Substantial increase in aircrew workload to recover from the resulting unusual attitude prior to departure from stable flight.
Unrestrained occupant injuries resulting from the abrupt attitude changes of the aircraft.
Analysis and Flt Test Figure AC 29 MG 21-1. Generic Examples by ATA.
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ATA 22-00-00 – AUTO FLIGHT SYSTEM ATA Function Description Failure Condition (FC) Phase of Operation Effect of the Failure on the Aircraft, Crew and Occupants Classification of the FC Notes (assumptions) Supporting Material Verification Method Malfunction (slowover) in a single axis.
Hover, TO App/Lnd Aircraft responds with a slow attitude change, resulting in an unusual attitude situation. This could result in an Analysis and Flt Test airspeed, attitude or yaw outside the approved limits (depart stabilized flight) or result in a ground impact.
Substantial increase in aircrew workload to recognize and recover from the resulting unusual attitude prior to departure from stable flight and without impacting the ground.
2212 Pitch Attitude Control Annunciated loss of pitch stabiliza tion.
ALL Aircraft reverts to unaugmented pitch control.
Slight increase in aircrew workload to maintain pitch attitude.
Occupants may encounter some slight discomfort.
Analysis and Flt Test Figure AC 29 MG 21-1. Generic Examples by ATA.
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AC 29-2C, Chg 7 2/4/2016 Note: Not all ATA chapters or subchapters have been included. Also, the italicized entries are not usually included in the failure condition description but in the systems description or assumptions section.
ATA 22-00-00 – AUTO FLIGHT SYSTEM ATA Function Description Failure Condition (FC) Phase of Operation Effect of the Failure on the Aircraft, Crew and Occupants Classification of the FC Notes (assumptions) Supporting Material Verification Method Unannunc iated loss of pitch stabiliza tion.
ALL Significant reduction in safety margins due to the delay in pilot reaction to take control.
Significant increase in aircrew workload due to the delayed recognition and recovery of pitch attitude.
Occupants may encounter some slight discomfort.
Analysis and Flt Test 2216 Autopilot Trim Loss of autopilot trim (IFR).
ALL Slight reduction in safety margins due to loss of finite control.
Aircrew workload may increase significantly due to loss of automatic control.
Occupants may encounter some slight discomfort.
Gnd and Flt Test Figure AC 29 MG 21-1. Generic Examples by ATA.
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ATA 22-00-00 – AUTO FLIGHT SYSTEM ATA Function Description Failure Condition (FC) Phase of Operation Effect of the Failure on the Aircraft, Crew and Occupants Classification of the FC Notes (assumptions) Supporting Material Verification Method Unannunci ated malfunction (runaway).
Hover, TO App/Lnd Aircraft responds with a rapid attitude change, resulting in a possible departure from stable flight, or impact with terrain or ground-based obstacles.
Substantial increase in aircrew workload to recover from the resulting unusual attitude.
Occupant injuries and possible death resulting from the abrupt attitude changes of the aircraft and possible ground impact.
Analysis and Flt Test Figure AC 29 MG 21-1. Generic Examples by ATA.
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AC 29-2C, Chg 7 2/4/2016 Note: Not all ATA chapters or subchapters have been included. Also, the italicized entries are not usually included in the failure condition description but in the systems description or assumptions section.
ATA 22-00-00 – AUTO FLIGHT SYSTEM ATA Function Description Failure Condition (FC) Phase of Operation Effect of the Failure on the Aircraft, Crew and Occupants Classification of the FC Notes (assumptions) Supporting Material Verification Method 2250 Aerody namic Load Alleviating (Stability Augmenta tion) Loss of stability augmenta tion (VFR).
Hover A significant reduction in system margins is expected because of the inherent instability of most rotorcraft in hover.
The aircraft will lose short-term stability requiring a significant increase in workload is expected to maintain control.
Occupant injuries resulting from the abrupt attitude changes of the aircraft and possible ground impact.
Gnd and Flt Test Figure AC 29 MG 21-1. Generic Examples by ATA.
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ATA 22-00-00 – AUTO FLIGHT SYSTEM ATA Function Description Failure Condition (FC) Phase of Operation Effect of the Failure on the Aircraft, Crew and Occupants Classification of the FC Notes (assumptions) Supporting Material Verification Method Unannunci ated loss of Hover The information to the flight crew could be Analysis and Flt Test stability delayed long enough for augmenta the aircraft to attain an tion (IFR). unusual attitude, which significantly reduces the safety margins or functional capabilities.
The aircrew workload would significantly increase in order to recognize and recover from an unusual attitude and regain stable flight.
Occupant injuries resulting from the abrupt attitude changes of the aircraft and possible ground impact.
Figure AC 29 MG 21-1. Generic Examples by ATA.
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AC 29-2C, Chg 7 2/4/2016 Note: Not all ATA chapters or subchapters have been included. Also, the italicized entries are not usually included in the failure condition description but in the systems description or assumptions section.
ATA 22-00-00 – AUTO FLIGHT SYSTEM ATA Function Description Failure Condition (FC) Phase of Operation Effect of the Failure on the Aircraft, Crew and Occupants Classification of the FC Notes (assumptions) Supporting Material Verification Method Malfunction (hardover) in a single axis.
Hover, TO App/Lnd Aircraft responds with a rapid attitude change, resulting in departure from stable flight and possible ground impact.
Analysis and Flt Test Substantial increase in aircrew workload to recover from the resulting unusual attitude prior to departure from stable flight and possible ground impact.
Occupant injuries and possible death resulting from the abrupt attitude changes of the aircraft and possible ground impact.
Figure AC 29 MG 21-1. Generic Examples by ATA.
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ATA 22-00-00 – AUTO FLIGHT SYSTEM ATA Function Description Failure Condition (FC) Phase of Operation Effect of the Failure on the Aircraft, Crew and Occupants Classification of the FC Notes (assumptions) Supporting Material Verification Method Malfunction (hardover) in a single axis.
Cruise Aircraft responds with a rapid attitude change, resulting in an unusual attitude or departure from stable flight.
The aircrew workload would significantly increase in order to recognize and recover from an unusual attitude and regain stable flight.
Analysis and Flt Test Figure AC 29 MG 21-1. Generic Examples by ATA.
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