As 2013 was poised to become 2014, the NTSB added five new subjects to its growing list of Safety Alerts aimed at general aviation pilots. The agency's interest in general aviation safety was underscored when in 2014 the Safety Board again included reducing general aviation accident rates on its list of most wanted safety improvements.
Since 2004, the NTSB has issued 25 Safety Alerts for general aviation dealing with subjects that come up from time to time in accident investigations. Exam-ples include: encountering in-flight icing, preventing stalls at low altitude and avoiding thunderstorms.
The five Safety Alerts issued on December 27, 2013, were: Check Your Restraints; Engine Power Loss Due to Carburetor Icing; "Armed" for Safety: Emer-gency Locator Transmitters; All Secure, All Clear (securing items in the aircraft cabin) and Proper Use of Fiber or Nylon Self-Locking Nuts.
The carburetor icing alert notes that on average, from 2000 through 2011, there were just over 20 accidents per year involving carburetor icing, two of which each year involved fatalities. The Safety Board says some pilots still erroneously believe that carburetor icing can only occur in cold or wet weather conditions. In addition, the Safety Board says that pilots don't promptly recognize the signs of carburetor icing and take action to use carburetor heat while it's still effective. The NTSB urges pilots to: "Check the temperature and dew point for your flight to determine whether the conditions are favorable for carburetor icing. Remember, serious carburetor icing can occur in ambient temperatures as high as 90° F, or in relative humidity conditions as low as 35 percent at glide power.
"Refer to your approved aircraft flight manual or operating handbook to ensure that you are using carburetor heat according to the approved procedures and properly perform the following actions: Check the functionality of the carburetor heat before your flight; Use carburetor heat to prevent the formation of carburetor ice when operating in conditions and at power settings in which carburetor icing is probable. Remember, ground idling or taxiing time can allow carburetor ice to accumulate before takeoff; Immediately apply carburetor heat at the first sign of carburetor icing, which typically includes a drop in rpm or manifold pressure (depending upon how your airplane is equipped). Engine roughness may follow."
In addition, the NTSB suggests that it would be a good idea to consider installing a carburetor temperature gauge if a retrofit is available for your particular aircraft model. The Safety Board also urges pilots whose engines use automotive gas to remember that they may be more susceptible to carburetor icing than engines that run on avgas. It points to a publication from Transport Canada, TP 10737, The Use of Automotive Gas (Mogas) in Aviation, as a good reference guide for pilots using automotive fuels.
The Safety Alert dealing with ELTs suggests pilots: "Confirm that the ELT unit is 'armed' and properly installed in the aircraft.
"Follow manufacturer instructions for properly securing the ELT and inspecting the fasteners.
"Remember that ELTs secured to the aircraft via Velcro®-style mounting mechanisms can be susceptible to strap looseness and misalignment during installation and inspection. Further, the retention straps may degrade over time due to wear, vibration, temperature or contamination, and they may not properly restrain the ELT during an accident.
"Consider upgrading to a 406-MHz ELT, which the NTSB has long recommended be mandatory due to its superior position accuracy reporting, timeliness of alerts and ability to provide aircraft identification and other information."
The Safety Alert on securing objects suggests that pilots: "Inspect the airplane for forgotten or misplaced tools before takeoff. Remember that even experienced pilots and aviation maintenance technicians can make mistakes. If you have recently had maintenance performed on your airplane or if you have conducted maintenance yourself, this action is especially important.
"Conduct an inventory of cockpit items before takeoff, including the number of personal electronic devices, GPS units and antennas on board the aircraft, and ensure that they are secured. This also helps to assure their availability throughout the flight.
"Account for all flight gear and personal items such as hats and jackets before and after each flight, and ensure that they are secured.
"Incorporate all of these checks into your preflight actions.
"Remind passengers during the preflight briefing of the importance of item security and proper stowage of PEDs and personal items."
In the Safety Alert "Check your Restraints," the Safety Board points out that although seat belts and harnesses have to be inspected as part of the annual, there's no easy way to tell whether they've deteriorated due to age, exposure to UV rays, contaminants and repeated use.
An accident that occurred in 2006 just off of Santa Monica, Calif., was highlighted. It involved a Beech A36 that was ditched in the ocean after the engine lost power during initial climb. A connecting rod had fractured from the crankshaft. The Safety Board said things began to unravel in the engine after a nut came off of its bolt because it hadn't been properly torqued, and no cotter pin had been installed to prevent it from backing off.
Both the pilot and passenger were killed, and the investigators said that a review of the autopsy results and impact damage to the wreckage indicated that had the occupants been restrained by shoulder harnesses, their chances of survival would have been a lot better. The airplane wasn't manufactured with shoulder harnesses, though there was the opportunity to do a subsequent installation. In June 1985, the manufacturer issued a mandatory Service Bulletin announcing the availability of shoulder harness kits for the model involved in the accident and many others. In September 1990, the Service Bulletin was revised to offer an incentive to owners who upgraded their airplanes with the shoulder harness kits prior to October 31, 1992.
The NTSB made note of an FAA publication discussing occupant protection for small airplanes (FAA document #AM-400-90/2). In it, the FAA reports that seat belts alone will only protect the occupant in very minor impacts, and that using shoulder harnesses in small aircraft would reduce injuries by 88% and fatalities by 20%.
Another accident cited by the NTSB in the Safety Alert on restraints involved a crop sprayer. The Piper PA-36-285 was conducting a Part 137 aerial application flight on October 18, 2008, at Silverton, Texas. The commercial pilot, who was the only occupant, was seriously injured in the accident. Physical evidence indicated that the airplane hit an electrical transmission wire. The airplane was equipped with a wire deflector, which was mounted on the cockpit windshield. The wire deflector was bent. In addition, an anti-snag deflector cable, which was supposed to run from the cockpit to the vertical fin, was torn immediately forward of the vertical fin. The spar caps on either side of the vertical spar displayed compression damage, and the spar web had been damaged. The rudder displayed compression wrinkling. The vertical stabilizer had separated from the airplane and wasn't recovered. Investigators determined that aircraft control wouldn't have been possible, and a crash was inevitable.
Investigators reported that the pilot's restraints were faded and appeared worn. The pilot's left lap belt had failed inboard of the adjustment buckle, with the failure area displaying signs of wear and stretching. The cable securing the shoulder harness to the inertial reel had failed just below the connection to the shoulder harness. No identification tags were found on the belt showing the date of manufacture. The airframe logbook showed that all of the restraint cables were replaced in 1997, and the center shoulder harness cable was replaced in 2000. There was no entry found for the replacement of the restraint webbing material.
In the Safety Alert dealing with "Proper Use of Fiber or Nylon Self-Locking Nuts," the Safety Board said that some pilots and mechanics aren't adequately inspecting the nuts they're installing to be sure their fiber or nylon inserts are in good condition and won't allow the nuts to loosen under in-flight vibration. The Safety Board notes that the ability of a self-locking nut to really lock degrades with each use. The Safety Board points to the 2011 crash of a North American P-51D into the crowd at the National Championship Air Races in Reno, Nev., as a worst-case example. The pilot and 10 people on the ground sustained fatal injuries, and at least 64 people on the ground were injured. As we previously reported in this column, the Safety Board found that reduced stiffness of the elevator trim tab system allowed aerodynamic flutter to occur at racing speeds. The reduced stiffness was a result of deteriorated locknut inserts that allowed the trim tab attachment screws to become loose and to initiate fatigue cracking in one screw sometime before the accident flight. Aerodynamic flutter of the trim tabs resulted in a failure of the left trim tab link assembly, elevator movement, high flight loads and a loss of control. Contributing to the accident were undocumented and untested major modifications to the airplane and the pilot's operation of the airplane in the unique air racing environment without adequate flight testing.
Peter Katz is editor and publisher of NTSB Reporter, an independent monthly update on aircraft accident investigations and other news concerning the National Transportation Safety Board. To subscribe, write to: NTSB Reporter, Subscription Dept., P.O. Box 831, White Plains, N.Y. 10602-0831.