05-20864. Special Conditions: Gulfstream Aerospace Limited Partnership (GALP) Model G150 Airplane; Windshield Coating in Lieu of Wipers

AGENCY:

Federal Aviation Administration (FAA), DOT.

ACTION:

Final special conditions.

SUMMARY:

These special conditions are issued for the Gulfstream Aerospace Limited Partnership (GALP) Model G150 airplane. This airplane will have a novel or unusual design feature associated with use of a hydrophobic coating, rather than windshield wipers, as the means to maintain a clear portion of the windshield during precipitation conditions, as required by the airworthiness standards for transport category airplanes. The applicable airworthiness regulations do not contain adequate or appropriate safety standards for this design feature. These special conditions contain the additional safety standards that the Administrator considers necessary to establish a level of safety equivalent to that established by the existing airworthiness standards.

EFFECTIVE DATE:

November 17, 2005.

FOR FURTHER INFORMATION CONTACT:

John McConnell, Airplane and Flight Crew Interface Branch, ANM-111, Transport Airplane Directorate, Aircraft Certification Service, 1601 Lind Avenue SW., Renton, Washington, 98055-4056; telephone [phone]; facsimile [phone], e-mail [e-mail].

SUPPLEMENTARY INFORMATION:

Background

On September 22, 2002, GALP applied for an amendment to Type Certificate Number A16NM to include the new GALP Model G150 airplane. The GALP Model G150, which is a derivative of the GALP Model G100 currently approved under Type Certificate Number A16NM, is intended to be a nine passenger executive airplane with a maximum takeoff weight of 26,000 pounds and a maximum operating altitude of 45,000 feet.

The GALP Model G150 flightdeck design incorporates a hydrophobic coating to provide adequate pilot compartment view in the presence of precipitation. Sole reliance on such a coating, without windshield wipers, constitutes a novel or unusual design feature for which the applicable airworthiness regulations do not contain adequate or appropriate safety standards. Therefore, special conditions are required that provide the level of safety equivalent to that established by the regulations.

Type Certification Basis

Under the provisions of 14 CFR 21.101, GALP must show that the Model G150 meets the applicable provisions of the regulations incorporated by reference in Type Certificate Number A16NM or the applicable regulations in effect on the date of application for the change to the type certificate. The regulations incorporated by reference in the type certificate are commonly referred to as the “original type certification basis.” The regulations incorporated by reference in Type Certificate Number A16NM are 14 CFR part 25, effective February 1, 1965, including Amendment 25-1 through Amendment 25-107.

In addition, if the regulations incorporated by reference do not provide adequate standards with respect to the change, the applicant must comply with certain regulations in effect on the date of application for the change. GALP has elected to voluntarily comply with Amendment 25-108 for the G150 type certification program.

If the Administrator finds that the applicable airworthiness regulations (i.e., 14 CFR part 25) do not contain adequate or appropriate safety standards for the Model G150 because of a novel or unusual design feature, special conditions are prescribed under the provisions of § 21.16.

In addition to the applicable airworthiness regulations and special conditions, the Model G150 must comply with (1) either the “No Acoustical Change” provisions of § 21.93(b) or 14 CFR part 36, as amended by Amendments 36-1 through 36-24, and (2) either the “No Emission Change” provisions of § 21.93(c) or 14 CFR part 34, as amended by Amendment 34-1 through Amendment 34-3.

Special conditions, as defined in 14 CFR 11.19, are issued in accordance with § 11.38 and become part of the type certification basis in accordance with § 21.101.

Special conditions are initially applicable to the model for which they are issued. Should the type certificate for that model be amended later to include any other model that incorporates the same or similar novel or unusual design feature, or should any other model already included on the same type certificate be modified to incorporate the same novel or unusual design feature, the special conditions would also apply to the other model under the provisions of § 21.101.

Novel or Unusual Design Features

The GALP Model G150 will incorporate the following novel or unusual design feature: Hydrophobic windshield coating as the sole means to maintain a clear portion of the windshield, during precipitation conditions, sufficient for both pilots to have a sufficiently extensive view along the flight path.

Discussion

Section 25.773(b)(1) requires that both pilots of a transport category airplane be provided a means to maintain a sufficiently clear portion of the windshield during precipitation conditions, and that this clear portion of the windshield must have a sufficiently extensive view along the flight path. The regulations require this means to maintain such an area during precipitation in heavy rain at speeds up to 1.5 V_SR1.

This requirement has existed in principle since 1953 in Part 4b of the Civil Air Regulations (CAR). Section 4b.351(b)(1) of CAR 4b required that “Means shall be provided for maintaining a sufficient portion of the windshield clear so that both pilots are afforded a sufficiently extensive view along the flight path in all normal flight attitudes of the airplane. Such means shall be designed to function under the following conditions without continuous attention on the part of the crew: (i) In heavy rain at speeds up to 1.6 V_S1, flaps retracted.” Effective December 26, 2002, Amendment 25-108, changed the speed for effectiveness of the means to maintain an area of clear vision from up to 1.6 V_S1 to 1.5 V_SR1 to accommodate the redefinition of the reference stall speed from the minimum speed in the stall, V_S1, to greater than or equal to the 1-g stall speed, V_SR1. As noted in the preamble to the final rule for that amendment, the reduced factor of 1.5 on V_SR1 is to maintain approximately the same speed as the 1.6 factor on V_S1.

The requirement that the means to maintain a clear area of forward vision must function at high speeds and high precipitation rates is based on the use of windshield wipers as the means to maintain an adequate area of clear vision in precipitation conditions. The requirement in 14 CFR 121.313(b), and in 14 CFR 125.213(b), to provide “a windshield wiper or equivalent for each pilot station” has remained unchanged since at least 1953.

The effectiveness of windshield wipers to maintain an area of clear vision normally degrades as airspeed and precipitation rates increase. It is assumed that because high speeds and high precipitation rates represent limiting conditions for windshield wipers, they will also be effective at lower speeds and precipitation levels. Accordingly, § 25.773(b)(1)(i) does not require maintenance of a clear area of forward vision at lower speeds or lower precipitation rates.

A forced airflow blown directly over the windshield has also been used to maintain an area of clear vision in precipitation. The limiting conditions for this technology are comparable to those for windshield wipers. Accordingly, introduction of this technology did not present a need for special conditions to maintain the level of safety embodied in the existing regulations.

Hydrophobic windshield coatings may depend to some degree on airflow directly over the windshield to maintain a clear vision area. The heavy rain and high-speed conditions specified in the current rule do not necessarily represent the limiting conditions for this new technology. For example, airflow over the windshield, which may be necessary to remove moisture from the windshield, may not be adequate to maintain a sufficiently clear area of the windshield in low speed flight or during ground operations. Alternatively, airflow over the windshield may be disturbed during such critical times as the approach to land, where the airplane is at a higher than normal pitch attitude. In these cases, areas of airflow disturbance or separation on the windshield could cause failure to maintain a clear vision area on the windshield.

In addition to potentially depending on airflow to function effectively, hydrophobic coatings may also be dependent on water droplet size for effective precipitation removal. For example, precipitation in the form of a light mist may not be sufficient for the coating's properties to result in maintaining a clear area of vision.

In summary, the current regulations identify speed and precipitation rate requirements that represent limiting conditions for windshield wipers and blowers, but not for hydrophobic coatings, so it is necessary to issue special conditions to maintain the level of safety represented by the current regulations.

These special conditions provide an appropriate safety standard for the hydrophobic coating technology as the means to maintain a clear area of vision by requiring it to be effective at low speeds and precipitation rates as well as the higher speeds and precipitation rates identified in the current regulation. These are the only new or changed requirements relative to those in § 25.773(b)(1) at Amendment 25-108.

Discussion of Comments

Notice of proposed special conditions No. 25-05-07 for the Gulfstream Aerospace Limited Partnership Model G150 airplane was published in the Federal Register on June 30, 2005 (70 FR 37715). Only one commenter responded to the notice.

Using Hydrophobic Coating Is Not Novel and Unusual

The commenter, Gulfstream, states that the FAA defines hydrophobic coating as “a novel and unusual design feature on one model of airplane.” The commenter notes that the hydrophobic coating proposed for the Model G150 has actually accumulated a significant service history and has been certified on numerous transport airplanes.

We infer that the commenter does not agree that the use of hydrophobic coating should be identified as “a novel and unusual design feature.” We do not agree. We believe that the previous approvals for using hydrophobic coating should have included special conditions in the type certification basis. As is the case for the Model G150, the use of hydrophobic coatings in lieu of windshield wipers represents a novel design feature relative to the certification basis of each of those airplane types. While the satisfactory service history indicates that these particular designs would likely have met the requirements of the special conditions, the existing regulatory requirements would not by themselves have necessarily assured the intended level of safety for the use of hydrophobic coating for precipitation removal for these designs, or for other designs. Special conditions are necessary to address the use of hydrophobic coating instead of windshield wipers. No changes were made as a result of this comment.

Sufficient View

The commenter recommends that the term “sufficient view” be changed to “sufficient view depending on aircraft speed.” The commenter states that the visibility requirements for taxi are different than the requirements for flight.

We do not agree with the commenter's recommendation. The existing regulatory requirements in 14 CFR 25.773(b)(1), at Amendment 25-108, do not explicitly include this qualification. As with the existing requirements, the interpretation of “sufficient view” in these special conditions may be dependent on several factors other than airplane speed, such as phase of flight or ground operations. No changes were made as a result of this comment.

Changes to the Proposed Special Conditions

The reference to “the flight path in normal flight attitudes of the airplane” has been changed to “the ground or flight path in normal taxi and flight attitudes of the airplane.” This change clarifies a possible ambiguity regarding the path of the airplane relative to the speeds necessary to maintain the clear vision area. While this additional language is absent from the requirement of § 25.773(b)(1), it is consistent with the intended level of safety. As noted in the Discussion section of the Notice of Proposed Special Conditions, the existing requirements are premised on the use of windshield wipers or other means for which slow speeds and minimal airflow are not limiting conditions for maintaining an area of clear vision. Hydrophobic coatings, however, are least effective at slow speeds and low airflow rates. To maintain the same level of safety as the existing regulations, the certification basis must address both ground and flight operations, as reflected by the speed and airflow range included in the proposed special conditions.

We also changed the Discussion section to correct the effective date of Amendment 25-108 from December 26, 1990, to December 26, 2002. In addition, we made editorial changes to the Discussion section to clarify certain information regarding airspeed. Except as discussed above, the special conditions are adopted as proposed.

Applicability

As discussed above, these special conditions are applicable to the Model G150. Should GALP apply at a later date for a change to the type certificate to include other type designs incorporating the same novel or unusual design feature, the special conditions would apply to those models as well under the provisions of § 21.101.

Conclusion

This action affects only certain novel or unusual design features on one model of airplane. It is not a rule of general applicability.

List of Subjects in 14 CFR Part 25

• Aircraft
• Aviation safety
• Reporting and recordkeeping requirements

The authority citation for these special conditions is as follows:

Authority: 49 U.S.C. 106(g), 40113, 44701, 44702, 44704.

The Special Conditions

Accordingly, pursuant to the authority delegated to me by the Administrator, the following special conditions are issued as part of the type certification basis for Gulfstream Aerospace Limited Partnership (GALP) Model G150 airplanes.

Pilot Compartment View—Hydrophobic Coatings in Lieu of Windshield Wipers

The airplane must have a means to maintain a clear portion of the windshield, during precipitation conditions, enough for both pilots to have a sufficiently extensive view along the ground or flight path in normal taxi and flight attitudes of the airplane. This means must be designed to function, without continuous attention on the part of the crew, in conditions from light misting precipitation to heavy rain at speeds from fully stopped in still air, to 1.5 V_SR1 with lift and drag devices retracted.

Issued in Renton, Washington, on October 7, 2005.

Kalene C. Yanamura,

Acting Manager, Transport Airplane Directorate, Aircraft Certification Service.