Exemption No. 11123 

UNITED STATES OF AMERICA 

DEPARTMENT OF TRANSPORTATION 

FEDERAL AVIATION ADMINISTRATION 

KANSAS CITY, MO 64106 

In the matter of the petition of 

HONDA AIRCRAFT COMPANY 

for an exemption from § 23.181 (b) of 

Title 14, Code of Federal Regulations 

Regulatory Docket No. FAA 2014-0700 

GRANT OF EXEMPTION 

By letter dated October 17, 2014, Mr. Randy Griffith, Certification Division Director, 

Honda Aircraft Company (Honda), 6430 Ballinger Road, Greensboro, NC 27410 petitioned 

the Federal Aviation Administration (FAA) on behalf of Honda for an exemption from 

§ 23.18l(b) ofTitle 14, Code of Federal Regulations (14 CFR). The proposed exemption, if 

granted, would allow the Honda Model HA-420 to be certified to use the Dutch roll damping 

requirements of 14 CFR 25.181(b), Dynamic Stability. 

The petitioner requests relief from the following regulation: 

Section 23.181 (b) states: 

"Any combined lateral-directional oscillations (Dutch roll) occurring between 

the stalling speed and the maximum allowable speed (V FE, V LE, V No, V FciMFc) 

appropriate to the configuration of the airplane with the primary controls in 

both free and fixed position, must be damped to 1/1 0 amplitude in: 

( 1) Seven (7) cycles below 18,000 feet and 

(2) Thirteen (13) cycles from 18,000 feet to the certified maximum altitude." 

The petitioner supports its request with the following information: 

The petitioner states: 

'The Part 23 requirement for Dutch roll oscillations to be damped to 1/ 10 

amplitude in 7 cycles was written, in part, as a result of few small airplanes 

having yaw damper systems. In contrast, nearly all current 14 CFR Part 23 jet 

ACE-14-487-E 
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airplanes are type certificated with yaw dampers since the ride quality must be 

tailored to maximize passenger comfort and safety. Part 25 airplanes are 

typically flown by pilots type rated for that specific airplane. Small, nonturbojet Part 23 airplanes generally do not require a type rating, and this is the 

reason that the Part 23 requirements are and should be more stringent for 

airplane handling characteristics. 

Larger aircraft typically employ a more complex "series" yaw damper that 

responds without causing rudder pedal motion. Series yaw damper 

engagement may be employed throughout all flight phases including landing 

and touchdown. The HA-420 airplane uses a conventional reversible rudder 

control system, manually cable-driven via the rudder pedals. The "parallel" 

yaw damper utilizes an electronic rudder servo, which generates torque, 

moving both the pilot's pedals and the rudder to augment stability. The yaw 

damper is typically engaged in flight to assist in suppressing the Dutch Roll 

mode. However, the yaw damper also tends to suppress pilot crosswind rudder 

inputs, and increase the rudder pedal forces required to generate those inputs. 

Therefore, the yaw damper is disengaged during takeoff and landing to 

minimize workload. 

The in-service history of the 4 flight test aircraft (Fl, F2, F3, and F4) as well 

as the first production aircraft (P 11) has shown that the airplane handling 

qualities are not objectionable with the yaw damper off during takeoff and 

landing. The quantitative analysis showed that the airplane damping is slightly 

less than the requirement to damp to 1/10 amplitude in 7 cycles at high field 

elevations." 

The FAA has determined that good cause exists for waiving the requirement for Federal 

Register publication because the exemption, if granted, would not set a precedent, and any 

delay in acting on this petition would be detrimental to Honda. 

The petitioner offers the following: 

"The Model HA-420 lateral-directional dynamic stability is positively damped 

and acceptable during expected operations with the yaw damper off. 

Operations of this type are very brief and are limited to a small fraction of the 

operational flight envelope." 

Mitigation discussion: 

• "Predictable handling qualities with well harmonized flight control forces. 

• The Airplane Flight Manual (AFM) will require the yaw damper to be 

engaged for all flight phases except takeoff and landing. 
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• The Crew Aletting System (CAS) logic will alett the crew, in the form of 

CAS messages, any time the yaw damper is not engaged during flight other 

than the takeoff and landing phases. 

• The yaw damper is automatically engaged after takeoff and will automatically 

disengage upon landing. The AFM procedure will direct the pilot to manually 

disengage the yaw damper prior to landing. 

• During the short duration that the yaw damper is not engaged during each 

flight, the pilot is fully in the airplane control loop. The un-augmented dynamic 

stability is positive and any unwanted residual oscillations are easily 

controllable by the pilot." 

The level of safety: 

• "The yaw damper is required by the AFM procedure and will provide a 

highly damped Dutch roll response for all flight phases when engaged. This 

will decrease pilot workload. 

• Testing shows that, in the unlikely event of a yaw damper failure, the 

autopilot roll channel provides highly damped Dutch roll response at all 

altitudes up to the maximum operating altitude. 

• In rare instances when neither autopilot nor yaw damper are available, the 

AFM will provide a maximum "retreat' altitude where natural Dutch roll 

damping meets the basic rule (damping to 1110 amplitude in 13 cycles). 

Company test have shown, and certification testing will verify that the aircraft 

can safely descend to this retreat altitude from maximum operating altitude, 

and also descend from the retreat altitude to landing. 

• Relative to the objectionable workload with a parallel yaw damper engaged, 

disengaging the yaw damper for crosswind or gusty takeoffs and landings 

enhances safety. 

• As part of flight testing using normal procedures, company test pilots and 

DER pilots evaluated numerous takeoff and landings with the yaw damper 

disengaged. Testing consistently showed that natural Dutch roll damping 

resulted in acceptable workload and did not adversely affect safety. 

Furthermore, in the course of certification testing, FAA pilots will have ample 

opportunity to evaluate and confirm workload acceptability across the spectrum 

of atmospheric conditions naturally found during flight testing." 
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Public interest and global considerations: 

• "For the airframe to inherently provide the required damping would result in 

a less fuel efficient design. The aircraft was designed to cruise efficiently at 

high speed and high altitude. When the necessary level of safety can be 

provided, maximum efficiency is in the public interest. 

• A more complex and expensive series yaw damper system design is not 

typical for this class of aircraft. Years of industry fleet experience with this 

style of yaw damper show that the necessary level of safety can be achieved. 

Minimizing expense and complexity are in the public interest. 

• The aircraft is marketing to a global customer base. Honda Aircraft Company 

will pursue foreign certifications shortly after receiving FAA certification. It is 

anticipated that our customers outside the United States will exercise the 

privileges of their certified aircraft, including this exemption, when travelling 

within their country of origin, as well as internationally. Honda will coordinate 

with the applicable foreign authorities for validation requirements related with 

this exemption." 

The FAA's analysis is as follows: 

The FAA finds that some part 25 and part 23 airplanes have been exempted from use of 

the yaw damper for takeoff and landing because the yaw damper can interfere with 

controllability in crosswinds. The FAA agrees with the petitioner's points and believes this is 

a reasonable exception to the Dutch roll requirements. Additionally, service experience of 

similar airplanes supports this exemption request. 

The FAA's Decision 

In consideration of the foregoing, I find that a grant of exemption is in the public interest 

and will not adversely affect safety. Therefore, pursuant to the authority contained 

in 49 U.S.C. §§ 106(f), 4011 3, and 44701, delegated to me by the Administrator, Honda 

Aircraft Company is granted an exemption from 14 CFR 23.181 (b) to the extent necessary to 

use 14 CFR 25.18l(b), Dynamic Stability Dutch roll damping requirements for their Model 

HA420 airplane certification basis, subject to the conditions and lin1itations listed below. 

Conditions and Limitations 

1. The Honda Model HA-420 yaw damper may be disabled for takeoff and landing, 

using part 25.181 (b) requirements instead of part 23.181 (b) requirements only for this phase 

of flight. 
Project No.: ACE-14-487-E 

Project Officer: Lowell Foster 

ACE-111 :Tiompkins: 11/26/14:Doc#xxxx 

(Insert Stylewriter Score Here] 

Randy Griffith 

Division Director, Certification 

Honda Aircraft Company 

6430 Ballinger Road 

Greensboro, NC 27410 

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2. A pilot evaluation must be made, with the yaw damper disabled during landing and 

takeoff, to verify that no unsafe condition exists with the airplane's handling characteristics. 

At least two Aircraft Certification test pilots and at least one Aircraft Evaluation Group 

(AEG) pilot should conduct the evaluation. 

Issued in Kansas City, MOon December 16 .2014 . 

Earl 

w~ 

Lawrence 

Manager, Small Aircraft Directorate 

Aircraft Certification Service 

• I( 
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2. A pilot evaluation must be made, with the yaw damper disabled during landing and 

takeoff, to verify that no unsafe condition exists with the airplane's handling characteristics. 

At least two Aircraft Certification test pilots and at least one Aircraft Evaluation Group 

(AEG) pilot should conduct the evaluation. 

Issued in Kansas City, MOon December 16 2014. 

Ea

w~ 

rl Lawrence 

Manager, Small Aircraft Directorate 

Aircraft Certification Service