Honda Aircraft Company Honda Aircraft Company 

'~'.,:: ,--~r: 6430 Ballinger Road 1

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. :,,>,·,:Greensboro, NC 27410 USA 

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; :Tel: 336.662.0246 

,~.! !u;F~x: 336.662.0852 

September 2, 2014 .. , .... ''I . . -.rr-._ 

,... '~:> i. 3\ GN-9438-14-009 

U.S. Department of Transportation 

Docket Operations 

West Building Ground Floor, Room W12-140 

1200 New Jersey Avenue, SE 

Washington, DC 20590 

Subject: Honda Aircraft Company Petition for Exemption to 14 CFR Part 23, 

§23.181(b) for the Honda Model HA-420 Dynamic Stability Compliance; FAA 

Project TC9438AT-A 

To whom it may concern, 

In accordance with 14 CFR Part 11, please find attached basis and information for Honda 

Aircraft Company's petition for an exemption to the requirements of 14t:FR .. Part-23,:·- ·:. 

§ 23.181(b) for the Honda Model HA-420 as related to dynamic stability compliance. 

The Model HA-420 is currently undergoing Type Certification, with the project managed 

by the Atlanta ACO. 

If you have any questions or comments on this request, please feel free to contact Mr. 

Karl Berg at (336) 662-0246 ext. 1022 or myself at (336) 662-0246 ext. 1670. 

Sincerely, 

Randy Griffith 

Honda Aircraft Company 

Division Director, Certification 

Enclosure 

Cc: 

Don Young, FAA Atlanta ACO 

HONDA 
----------------------------------

SUBJECT: Dynamic Stability Compliance (Request for Exemption). 

STATEMENT OF ISSUE: 

Honda Aircraft Company (Honda) located in Greensboro, North Carolina would like to use 

the Dutch roll damping requirements of 14 CFR Part 25.181 (b) Dynamic Stability to show 

regulatory compliance for certification of the HA-420 airplane during takeoff prior to the 

initiation of landing gear retraction and during landing with the airplane configured for 

landing. An exemption using a pilot evaluation is requested to confirm that no unsafe 

condition exists with the airplane's handling characteristics with the yaw damper 

disengaged during takeoff and landing. The Dutch roll damping requirements of 14 CFR 

Part 23.181(b) at Amendment 23-62 would be met for the majority of the envelope 

including takeoff and landing at field elevations below approximately 5,000 feet. 

BACKGROUND: 

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 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, 

non-turbojet 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. 

The HA-420 airplane uses a conventional reversible rudder control system, manually 

cable-driven via the rudder pedals. The yaw damper utilizes an electronic rudder servo, 

which generates torque that is in-series with the pilot's pedal inputs to drive the rudder and 

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. 

Many Part 23 and Part 25 airplanes equipped with a yaw damper do not allow its use 

during takeoff and landing because the yaw damper can interfere with controllability in 

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

facilitate crosswind control inputs. 

The in-service history of the 4 flight test aircraft (F1, F2, F3 and F4) as well as the first 

production aircraft (P11) 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. 

CONCLUSION: 

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. 

The reduced damping of the non-augmented airplane is mitigated by the following 

compensating features: 

• 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. 

• The Crew Alerting System (CAS) logic will alert 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 at 50 feet just prior to reducing thrust to idle. 

• 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. 

Based upon these compensating features, Honda believes an exemption to 14 CFR 

23.181(b) Arndt 23-62 is warranted for the HA-420.