AD 96-03-04 ACTIVE

This amendment adopts a new airworthiness directive (AD), applicable to various General Dynamics (Convair) airplanes, that requires revising the Airplane Flight Manual to require that the flight crew limit the flap settings during certain icing conditions and air temperatures. This amendment is prompted by reports indicating that incidents involving uncommanded pitch excursions have occurred due to ice contaminated tailplane stall (ICTS) that occurred during or following flight in icing conditions. If flap settings are increased for landing when conditions for ICTS are present, elevator control could be affected adversely and the airplane could descend uncontrollably. The actions specified by this AD are intended to ensure that the flight crew is advised of the potential hazard related to increasing the flap settings when conditions for ICTS are present, and the procedures necessary to address it.

Final rule

96-03-04 GENERAL DYNAMICS (CONVAIR): Amendment 39-9501. Docket 95-NM-19-AD.
Applicability: All Model 240 series airplanes, including Model T-29 (military) airplanes; Model 340 and 440 series airplanes; and Model C-131 (military) airplanes; including those models modified for turbo-propeller power (commonly referred to as Model 580, 600, and 640 series airplanes); certificated in any category.

Compliance: Required as indicated, unless accomplished previously.

To ensure that the flight crew is advised of the potential hazard associated with increasing the flap settings when ice contaminated tailplane stall (ICTS) conditions are present, and the procedures necessary to address it, accomplish the following:

(a) Within 30 days after the effective date of this AD, revise the Limitations Section of the FAA-approved Airplane Flight Manual (AFM) to include the following procedures, which will limit the flap settings during certain icing conditions and air temperatures.This may be accomplished by inserting a copy of this AD in the AFM.

"FLAP LIMITATION IN ICING CONDITIONS
Flap selection is limited to a maximum of 30 degrees after icing conditions have been
encountered; or when icing conditions are anticipated during approach and landing; or
when the outside air temperature is +5 degrees Celsius or below and any visible moisture
is present."

(b) An alternative method of compliance or adjustment of the compliance time that provides an acceptable level of safety may be used if approved by the Manager, Los Angeles Aircraft Certification Office (ACO), FAA, Transport Airplane Directorate. Operators shall submit their requests through an appropriate FAA Principal Maintenance Inspector, who may add comments and then send it to the Manager, Los Angeles ACO.

NOTE: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Los Angeles ACO.

(c) Special flight permits may be issued in accordance with sections 21.197 and 21.199 of the Federal Aviation Regulations (14 CFR 21.197 and 21.199) to operate the airplane to a location where the requirements of this AD can be accomplished.

(d) This amendment becomes effective on February 28, 1996.

A proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) to include an airworthiness directive (AD) that is applicable to various General Dynamics (Convair) airplanes was published in the Federal Register on June 16, 1995 (60 FR 31648). That action proposed to require revising the FAA-approved Airplane Flight Manual (AFM) to require that the flight crew limit the flap settings during certain icing conditions and air temperatures.

Interested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the comments received.

One commenter supports the proposed rule.

One commenter supports the proposed rule, but believes that an allowance should be made for using a setting of greater than flaps 30 after icing conditions have been encountered if outside air temperatures in the landing area are well above freezing. The commenter indicates that icing conditions may be encountered at cruising altitudes, but the ground temperatures could be much warmer. The commenter believes that there is virtually no chance that ice would remain on the tail. From the commenter's experience, all ice that has collected on the wing leading edges, engine nacelles, windscreens, and windshield wipers will have disappeared by the time the indicating outside air temperature has reached +5 degrees Celsius on descent.

In light of these remarks, the commenter suggests that the AFM revision required by paragraph (a) of the proposed rule be reworded as follows:

"Flap selection is limited to a maximum of 30 degrees after icing conditions have been encountered if the indicated OAT on approach is +5 degrees Celsius or lower; or if icing conditions are anticipated during approach and landing; or when the outside air temperature is +5 degrees Celsius or below and any visible moisture is present."

The FAA does not concur with the commenter's suggestion. Operators cannot generally assume that accreted ice will not be present on wings and tailplanes if the outside air temperatures are above +5 degrees Celsius on approach. Ice sublimation, melting, and shedding are not only functions of temperature, but also are dependent upon other factors such as the nature, size, and extent of ice accretion; operation of ice protection systems; time of flight in temperatures above freezing; and airplane speed.

The commenter's concern regarding incurring a flap extension limitation after encountering, and then departing, icing conditions has merit. However, the airplane must be free of ice before the flaps are extended to greater than 30 degrees. Since ice can accrete on tailplanes with a small leading edge radius when there is no evidence of ice accretion on the wings, a method of visual inspection of the wings, tailplanes, and/or proven ice detectors or ice evidence probes would be necessary to assure clean surfaces.

One commenter requests that the proposed AD be withdrawn. The commenter states that the airplane can be operated quite safely within the environment to which it is certified when the anti-icing system is operational and functioning, and when that system is used in the manner in which it was intended.

The FAA does not concur with the commenter's request. Test pilots of Convair Model 5800 series airplanes actually experienced evidence of ice contaminated tailplane stall (ICTS) during pushover maneuver flight tests. (Model 5800 series airplanes are similar to Model 340 series airplanes equipped with turbo-prop engines.) For this reason the type certificate holder agreed with the FAA that a flap extension restriction during operation in icing conditions is necessary. The specific flight test used to determine susceptibility to ICTS is a pushover maneuver to generate an increased angle of attack on the horizontal tailplane. This maneuver is performed with ice shapes on the tailplane and flaps in approach andlanding positions, at speeds from near approach to maximum for the configurations. The test procedure requires a push force throughout the maneuver to zero load factor. A force reversal would be indicative of an elevator hinge moment reversal caused by airflow separation due to accreted ice and an increased angle of attack due to pitch rate, and would define the aircraft as susceptible to ICTS. Because all affected Convair airplane models have designs that are essentially similar to the model tested, this AD requires a flap limitation.

The FAA has revised this final rule to clarify that the unsafe condition specified in this AD can occur if the flap settings are increased when conditions for ICTS are present.

After careful review of the available data, including the comments noted above, the FAA has determined that air safety and the public interest require the adoption of the rule as proposed.

There are approximately 282 Model 240 series airplanes, including Model T-29(military) airplanes; Model 340 and 440 series airplanes; Model C-131 (military) airplanes, and those models modified for turbo-propeller power; of the affected design in the worldwide fleet. The FAA estimates that 197 airplanes of U.S. registry will be affected by this AD, that it will take approximately 1 work hour per airplane to accomplish the required actions, and that the average labor rate is $60 per work hour. Based on these figures, the cost impact of the AD on U.S. operators is estimated to be $11,820, or $60 per airplane.

The cost impact figure discussed above is based on assumptions that no operator has yet accomplished any of the requirements of this AD action, and that no operator would accomplish those actions in the future if this AD were not adopted.

The regulations adopted herein will not have substantial direct effects on the States, on the relationship between the national government and the States, or on the distribution of power and responsibilities among the various levels of government. Therefore, in accordance with Executive Order 12612, it is determined that this final rule does not have sufficient federalism implications to warrant the preparation of a Federalism Assessment.

For the reasons discussed above, I certify that this action (1) is not a "significant regulatory action" under Executive Order 12866; (2) is not a "significant rule" under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and (3) will not have a significant economic impact, positive or negative, on a substantial number of small entities under the criteria of the Regulatory Flexibility Act. A final evaluation has been prepared for this action and it is contained in the Rules Docket. A copy of it may be obtained from the Rules Docket at the location provided under the caption "ADDRESSES."

List of Subjects in 14 CFR Part 39
Air transportation, Aircraft, Aviation safety, Safety.

Adoption of the Amendment
Accordingly, pursuantto the authority delegated to me by the Administrator, the Federal Aviation Administration amends part 39 of the Federal Aviation Regulations (14 CFR part 39) as follows:

PART 39 - AIRWORTHINESS DIRECTIVES
1. The authority citation for part 39 continues to read as follows:
Authority: 49 USC 106(g), 40113, 44701.

39.13 - [Amended]
2. Section 39.13 is amended by adding the following new airworthiness directive:

Information pertaining to this rulemaking action may be examined at the Federal Aviation Administration (FAA), Transport Airplane Directorate, Rules Docket, 1601 Lind Avenue, SW., Renton, Washington; or at the FAA, Los Angeles Aircraft Certification Office, Transport Airplane Directorate, 3960 Paramount Boulevard, Lakewood, California.

Andrew Gfrerer, Aerospace Engineer, Systems and Equipment Branch, ANM-130L, FAA, Transport Airplane Directorate, Los Angeles Aircraft Certification Office, 3960 Paramount Boulevard, Lakewood, California 90712; telephone (310) 627-5338; fax (310) 627-5210.