Airworthiness Directive · Amendment 39-11585 · McDonnell Douglas Models DC-3 and DC-4 Series Airplanes
McDonnell Douglas Models DC-3 and DC-4 Series Airplanes
Models DC-3 and DC-4 series airplanes equipped with pneumatic deicing boots, certificated in any category.
This amendment adopts a new airworthiness directive (AD), applicable to certain McDonnell Douglas Models DC-3 and DC-4 series airplanes that requires an inspection to determine the type of airframe pneumatic deicing boots installed. This amendment also requires revising the Airplane Flight Manual (AFM) to include requirements for activation of the pneumatic deicing boots for those airplanes equipped with "modern" boots. This amendment is prompted by reports of inflight incidents and an accident that occurred in icing conditions where the airframe pneumatic deicing boots were not activated. The actions specified by this AD are intended to ensure that flightcrews activate the pneumatic wing and tail deicing boots at the first signs of ice accumulation. This action will prevent reduced controllability of the aircraft due to adverse aerodynamic effects of ice adhering to the airplane prior to the first deicing cycle.
To ensure that flightcrews activate the wing and tail pneumatic deicing boots at the first signs of ice accumulation on the airplane, accomplish the following:
Note 1: For the purposes of this AD, the following definitions of “older” and “modern” apply:
“Modern” pneumatic boot systems may be characterized by short segmented, small diameter tubes, which are operated at relatively high pressures [18-23 pounds per square inch (psi)] by excess bleed air that is provided by turbine engines. “Older” pneumatic boot systems may be characterized by long, uninterrupted, large diameter tubes, which were operated at low pressures by engine driven pneumatic pumps whose pressure varied with engine revolutions per minute (rpm). This low pressure coupled with long and large diameter tubes caused early de-ice systems to have very lengthy inflation and deflation cycles and dwell times. (Dwell time is the period of time that the boot remains fully expanded following the completion of the inflation cycle until the beginning of the deflation cycle.)
(a) Within 10 days after the effective date of this AD: Perform a visual inspection to determine if the type of pneumatic deicing boots installed is either “older” or “modern” boots.
Note 2: For the purposes of this AD, a detailed visual inspection is defined as: “An intensive visual examination of a specific structural area, system, installation, or assembly to detect damage, failure, or irregularity. Available lighting is normally supplemented with a direct source of good lighting at intensity deemed appropriate by the inspector. Inspection aids such as mirror, magnifying lenses, etc., may be used. Surface cleaning and elaborate access procedures may be required.”
(1) For those airplanes equipped with “older” pneumatic deicing boots, no further action is required by this AD.
(2) For those airplanes equipped with “modern” pneumatic deicing boots, within 10 days after the inspection required by paragraph (a) of this AD: Revise the Limitations Section of the FAA-approved Airplane Flight Manual (AFM) to include the following requirements for activation of the ice protection systems. This may be accomplished by inserting a copy of this AD in the AFM.
“• Except for certain phases of flight where the AFM specifies that deicing boots should not be used (e.g., take-off, final approach, and landing), compliance with the following is required.
• Wing and Tail Leading Edge Pneumatic Deicing Boot System, if installed, must be activated:
—At the first sign of ice formation anywhere on the aircraft, or upon annunciation from an ice detector system, whichever occurs first; and
—The system must either be continued to be operated in the automatic cycling mode, if available; or the system must be manually cycled as needed to minimize the ice accretions on the airframe.
• The wing and tail leading edge pneumatic deicing boot system may be deactivated only after leaving icing conditions and after the airplane is determined to be clear of ice.”
