[Federal Register Volume 71, Number 60 (Wednesday, March 29, 2006)]
[Rules and Regulations]
[Pages 15557-15559]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 06-3013]



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  Federal Register / Vol. 71, No. 60 / Wednesday, March 29, 2006 / 
Rules and Regulations  

[[Page 15557]]



DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 27

[Docket No. SW013; Special Condition No. 27-013-SC]


Special Condition: Robinson R44 Helicopters, Sec.  27.1309, 
Installation of an Autopilot (AP) Stabilization Augmentation System 
(SAS) That Has Potential Failure Modes With Criticality Categories 
Higher Than Those Envisioned by the Applicable Airworthiness 
Regulations

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final special condition.

-----------------------------------------------------------------------

SUMMARY: This special condition is issued for the modification of the 
Robinson Model R44 helicopter. This modification will have novel or 
unusual design features associated with installing a complex Autopilot/
Stabilization Augmentation System (AP/SAS) that has potential failure 
modes with more severe adverse consequences than those envisioned by 
the existing applicable airworthiness regulations. This proposal 
contains the additional safety standards that the Administrator 
considers necessary to ensure that the failures and their effects are 
sufficiently analyzed and contained.

DATES: Effective Date: April 28, 2006.

FOR FURTHER INFORMATION CONTACT: Robert McCallister, Aviation Safety 
Engineer, FAA, Rotorcraft Directorate, Rotorcraft Standards Staff, 2601 
Meacham Blvd., Fort Worth, Texas 76193-0110; telephone (817) 222-5121, 
FAX (817) 222-5961.

SUPPLEMENTARY INFORMATION: 

Background

    On January 18, 2000, Hoh Aeronautics, Inc. submitted an application 
for a Supplemental Type Certification (STC) for the installation of an 
Autopilot Stability/Augmentation System (AP/SAS) on a Robinson Model 
R44 helicopter through the FAA's Los Angles Aircraft Certification 
Office (LA ACO). The Robinson Model R44 helicopter is a part 27 Normal 
category, single reciprocating engine, conventional helicopter designed 
for civil operation. The helicopter is capable of carrying three 
passengers with one pilot, and has a maximum gross weight of 
approximately 2,400 pounds. The major design features include a 2-
blade, fully articulated main rotor, a 2-blade anti-torque tail rotor, 
a skid landing gear, and a visual flight rule (VFR) basic avionics 
configuration. Hoh Aeronautics, Inc. proposes to install a three-axis 
AP/SAS.

Type Certification Basis

    Under the provisions of 14 CFR 21.115, Hoh Aeronautics, Inc. must 
show that the Robinson Model R44 helicopter, as modified by the 
installed AP/SAS, meets 14 CFR 21.101 standards. The baseline of the 
certification basis for the unmodified R44 is listed in Type 
Certification Data Sheet Number H11NM, Revision 3. Additionally, 
compliance must be shown to any special conditions prescribed by the 
Administrator.
    If the Administrator finds that the applicable airworthiness 
regulations, as they pertain to this STC, do not contain adequate or 
appropriate safety standards because of a novel or unusual design 
feature, special conditions are prescribed under the provisions of 
Sec.  21.101(d).
    In addition to the applicable airworthiness regulations and special 
conditions, Hoh Aeronautics, Inc. must show compliance of the AP/SAS 
STC-altered Robinson Model R44 helicopter with the noise certification 
requirements of 14 CFR part 36; and the FAA must issue a finding of 
regulatory adequacy pursuant to 49 U.S.C. 44715 (formerly Sec.  611 of 
the Federal Aviation Act of 1958 as amended by section 7 of Pub. L. 92-
574, the ``Noise Control Act of 1972'').
    Special conditions, as appropriate, are defined in Sec.  11.19, and 
issued by following the procedures in Sec.  11.38 and become part of 
the type certification basis in accordance with Sec.  21.101.
    Special conditions are initially applicable to the model for which 
they are issued. Should Hoh Aeronautics, Inc. apply for a supplemental 
type certificate to modify any other model included on the same type 
certificate to incorporate the same or similar novel or unusual design 
feature, the special condition would also apply to the other model 
under the provisions of Sec.  21.101.

Novel or Unusual Design Features

    The Hoh Aeronautics, Inc. AP/SAS system incorporates novel or 
unusual design features, for installation in a Robinson Model R44 
helicopter, Type Certification Data Sheet Number H11NM. This AP/SAS 
system performs non-critical control functions, since this model 
helicopter has been certificated to meet the applicable requirements 
independent of this system. However, the possible failure modes for 
this system, and their effect on the helicopter's ability to continue 
safe flight and landing, are more severe than those envisioned by the 
present rules when they were first promulgated.

Discussion of Comments

    Notice of proposed special condition No. 27-013-SC for the Robinson 
R44 Helicopter was published in the Federal Register on June 8, 2005 
(70 FR 33399). No comments were received on the special condition as 
proposed. After careful review of the available data, the FAA has 
determined that air safety and the public interest require the adoption 
of the special condition with only minor, non-substantive changes.

Definitions

    Definitions of Failure Condition Categories--Failure Conditions are 
classified, according to the severity of their effects on the aircraft, 
into one of the following categories:
    1. No Effect--Failure Conditions that would have no effect on 
safety; for example, Failure Conditions that would not affect the 
operational capability of the rotorcraft or increase crew workload; 
however, could result in an inconvenience to the occupants, excluding 
the flight crew.
    2. Minor--Failure conditions which would not significantly reduce 
rotorcraft safety, and which would involve crew actions that are well 
within their capabilities. Minor failure conditions may include, for 
example, a slight reduction in safety margins or functional 
capabilities, a slight increase in crew workload, such as routine 
flight

[[Page 15558]]

plan changes, or some physical discomfort to occupants.
    3. Major--Failure conditions which would reduce the capability of 
the rotorcraft or the ability of the crew to cope with adverse 
operating conditions to the extent that there would be, for example, a 
significant reduction in safety margins or functional capabilities, a 
significant increase in crew workload or in conditions impairing crew 
efficiency, physical distress to occupants, possibly including 
injuries, or physical discomfort to the flight crew.
    4. Hazardous/Severe-Major--Failure conditions which would reduce 
the capability of the rotorcraft or the ability of the crew to cope 
with adverse operating conditions to the extent that there would be:
     A large reduction in safety margins or functional 
capabilities;
     Physical distress or excessive workload that would impair 
the flight crew's ability to the extent that they could not be relied 
on to perform their tasks accurately or completely; or,
     Possible serious or fatal injury to a passenger or a cabin 
crewmember, excluding the flight crew.


    Note: ``Hazardous/Severe-Major'' failure conditions can include 
events that are manageable by the crew by use of proper procedures, 
which, if not implemented correctly or in a timely manner, may 
result in a Catastrophic Event.


    5. Catastrophic--Failure Conditions which would result in multiple 
fatalities to occupants, fatalities or incapacitation to the flight 
crew, or result in loss of the rotorcraft.
    The present Sec. Sec.  27.1309 (b) and (c) regulations do not 
adequately address the safety requirements for systems whose failures 
could result in ``Catastrophic'' or ``Hazardous/Severe-Major'' failure 
conditions, or for complex systems whose failures could result in 
``Major'' failure conditions. The current regulations are inadequate 
because when Sec. Sec.  27.1309(b) and (c) were promulgated, it was not 
envisioned that this type of rotorcraft would use systems that are 
complex or whose failure could result in ``Catastrophic'' or 
``Hazardous/Severe-Major'' effects on the rotorcraft. This is 
particularly true with the application of new technology, new 
application of standard technology, or other applications not 
envisioned by the rule that affect safety.
    We require that Hoh Aeronautics, Inc. provide the FAA with a 
Systems Safety Assessment (SSA) for the final AP/SAS installation 
configuration that will adequately address the safety objectives 
established by the Functional Hazard Assessment (FHA) and the 
Preliminary System Safety Assessment (PSSA), including the Fault Tree 
Analysis (FTA). This will ensure that all failure modes and their 
resulting effects are adequately addressed for the installed AP/SAS. 
The SSA process, FHA, PSSA, and FTA are all parts of the overall Safety 
Assessment (SA) process discussed in FAA Advisory Circular (AC) 27-1B 
(Certification of Normal Category Rotorcraft) and SAE document ARP 4761 
(Guidelines and Methods for Conducting the Safety Assessment Process on 
civil airborne Systems and Equipment).

Requirements

    We require that the applicant comply with the existing requirements 
of Sec.  27.1309 for all applicable design and operational aspects of 
the AP/SAS with the failure condition categories of ``No Effect,'' and 
``Minor,'' and for non-complex systems whose failure condition category 
is classified as ``Major.'' We require that the applicant comply with 
the requirements of this special condition for all applicable design 
and operational aspects of the AP/SAS with the failure condition 
categories of ``Catastrophic'' and ``Hazardous Severe/Major,'' and for 
complex systems whose failure condition category is classified as 
``Major.''


    Note: A complex system is a system whose operations, failure 
modes, or failure effects are difficult to comprehend without the 
aid of analytical methods (e.g., Fault Tree Analysis, Failure Modes 
and Effect Analysis, Functional Hazard Assessment, etc.).

Design Integrity Requirements

    Each of the failure condition categories defined in this special 
condition relate to corresponding aircraft systems integrity 
requirements. The systems design integrity requirements, for the Hoh 
Aeronautics, Inc. AP/SAS, as they relate to the allowed probability of 
occurrence for each failure condition category, along with the proposed 
software design assurance level, are as follows:
     ``Major''--Failures resulting in Major effects must be 
shown to be improbable, or on the order of 1 x 10-5 
failures/hour, and associated software must be developed to the RTCA/
DO-178B (Software Considerations in Airborne Systems And Equipment 
Certification) Level C software design assurance level.
     ``Hazardous/Severe-Major''--Failures resulting in 
Hazardous/Severe-Major effects must be shown to be extremely remote, or 
on the order of 1 x 10-7 failures/hour, and associated 
software must be developed to the RTCA/DO-178B (Software Considerations 
in Airborne Systems And Equipment Certification) Level B software 
assurance level.
     ``Catastrophic''--Failures resulting in Catastrophic 
effects must be shown to be extremely improbable, or on the order of 1 
x 10-\9\ failures/hour, and associated software must be 
developed to the RTCA/DO-178B (Software Considerations in Airborne 
Systems And Equipment Certification) Level A design assurance level.

Design Environmental Requirements

    We require that the AP/SAS system equipment be qualified to the 
appropriate environmental level in the RTCA document DO-160D 
(Environmental Conditions and Test Procedures for Airborne Equipment), 
for all relevant aspects. This is to ensure that the AP/SAS system 
performs its intended function under any foreseeable operating 
condition, which includes the expected environment in which the AP/SAS 
is intended to operate. Some of the main considerations for 
environmental concerns are installation locations and the resulting 
exposure to environmental conditions for the AP/SAS system equipment, 
including considerations for other equipment that may be affected 
environmentally by the AP/SAS equipment installation. The level of 
environmental qualification must be related to the severity of the 
considered failure effects on the aircraft.

Test & Analysis Requirements

    Compliance with the requirements contained in this special 
condition may be shown by a variety of methods, which typically consist 
of analysis, flight tests, ground tests, and simulation, as a minimum. 
Compliance methodology is partly related to the associated failure 
condition category. If the AP/SAS is a complex system, compliance with 
the requirements contained in this document for aspects of the AP/SAS 
that can result in failure conditions classified as ``Major'' may be 
shown by analysis, in combination with appropriate testing to validate 
the analysis. Compliance with the requirements contained in this 
special condition for aspects of the AP/SAS that can result in failure 
conditions classified as ``Hazardous/Severe-Major'' may be shown by 
flight-testing in combination with analysis and simulation, and the 
appropriate testing to validate the analysis. Flight tests may be 
limited for this classification of failures due to safety 
considerations.

[[Page 15559]]

Compliance with the requirements contained in this special condition 
for aspects of the AP/SAS that can result in failure conditions 
classified as ``Catastrophic'' may be shown by analysis, and 
appropriate testing in combination with simulation to validate the 
analysis. Very limited flight tests in combination with simulation are 
typically used as a part of a showing of compliance for failures in 
this classification. Flight tests are performed only in circumstances 
that use operational variations, or extrapolations from other flight 
performance aspects to address flight safety.
    This special condition requires that the AP/SAS system installed on 
a Robinson Model R44 helicopter, Type Certification Data Sheet Number 
H11NM, Revision 3, meet these requirements to adequately address the 
failure effects identified by the FHA, and subsequently verified by the 
SSA, within the defined design integrity requirements.

Applicability

    This special condition is applicable to the Hoh Aeronautics, Inc. 
AP/SAS installed as an STC approval, in a Robinson Model R44 
helicopter, Type Certification Data Sheet Number H11NM, Revision 3.

Conclusion

    This action affects only certain novel or unusual design features 
for a Hoh Aeronautics, Inc. AP/SAS STC installed on one model series of 
helicopter. It is not a rule of general applicability and affects only 
the applicant who applied to the FAA for approval of these features on 
the helicopter.

List of Subjects in 14 CFR Part 27

    Aircraft, Air transportation, Aviation safety, Rotorcraft, Safety.

    The authority citation for this special condition is as follows:

    Authority: 42 U.S.C. 7572, 49 U.S.C. 106(g), 40105, 40113, 
44701-44702, 44704, 44709, 44711, 44713, 44715, 45303.

Final Special Condition Information

The Special Condition

    Accordingly, pursuant to the authority delegated to me by the 
Administrator, the following special condition is issued as part of the 
Hoh Aeronautics, Inc. supplemental type certificate basis for an 
Autopilot/Stability Augmentation System to be installed on a Robinson 
Model R44 helicopter, Type Certification Data Sheet Number H11NM, 
Revision 3.
    The Autopilot/Stability Augmentation System must be designed and 
installed so that the failure conditions identified in the Functional 
Hazard Assessment and verified by the System Safety Assessment, after 
design completion, are adequately addressed in accordance with the 
``Definitions'' and ``Requirements'' sections (including the design 
integrity, design environmental, and test and analysis requirements) of 
this special condition.

    Issued in Fort Worth, Texas, on March 21, 2006.
David A. Downey,
Manager, Rotorcraft Directorate, Aircraft Certification Service.
[FR Doc. 06-3013 Filed 3-28-06; 8:45 am]
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