On Sunday, daylight savings time ended, and the reality of less daylight is evident in the colder weather we are experiencing. October’s blog article discussed frost and polished frost. November brings cooler nights and a higher likelihood for much of the lower 48 of experiencing freezing rain or even snow. If your aircraft is parked outside, you should inspect all the airfoils to ensure there isn’t frost or snow. Remember, all surfaces are critical and should remain free of contaminates! But how should you perform this inspection?
A Case Study (Accident Number: LAX95LA038)
On November 22, 1994, at 0720 Pacific standard time, a Cessna T210H, N2221R, operated by the pilot, collided with terrain during an initial climb from a private airstrip about 5 miles east of Mount Hamilton, California. The private pilot and three passengers received minor injuries.
The pilot reported that the accident airplane had been parked overnight at the airstrip. The pilot stated that he did not have a ladder, and the airplane was not equipped with fuselage footsteps. However, during the preflight inspection, he did observe an accumulation of frost on the front windshield. So, prior to taking off, he scraped some of it off to enhance his visibility.
The pilot stated that the airplane stopped climbing after reaching a maximum altitude between 100 and 200 feet above ground level. The engine then seemed to lose power. The airplane stalled and collided with terrain adjacent to the western side of the airstrip. The pilot estimated that when he commenced the takeoff the outside air temperature was between 30 and 32 degrees Fahrenheit.
In the pilot’s completed “Aircraft Accident Report,” NTSB Form 6120.1, he reported that during his preflight inspection, “there was ice buildup on the windshield,” and ” . . . no noticeable ice on the flaps, horizontal stabilizer or on the fuselage . . . . ” During the takeoff roll, “there was no ice formation on the windshield or anything unusual at that time.”
The pilot provided the following additional chronology of events regarding the start of the accident flight: “I held the aircraft on the ground for until (sic) I reached about 80 MPH and then I rotated. I established a normal rate of climb. At the time of rotation, the windshield began to glaze over and by the time I had climbed to approximately 100 feet AGL my forward visibility was about zero. I raised the nose for a few seconds in order to be sure to clear the obstacles that I knew were at the end of the runway. There was no stall warning nor did the aircraft attitude seem to be too high to me. At this time the engine seemed as if it were only performing at approximately sixty (60%) of its power capability.”
According to the FAA coordinator, one of the passengers reported that the engine sound did not change from the time full power was applied, at the beginning of the takeoff, until ground impact. Also, the airplane’s takeoff seemed normal until reaching an altitude of approximately 100 feet when he felt the airplane was sinking from under him. The passenger reported that he observed frost on the exposed upper surfaces of the aircraft in addition to the front and rear windshields prior to takeoff.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: the pilot’s failure to obtain/maintain an adequate airspeed and inadvertent entry into a stall/mush condition during the initial climb due to frost on the airframe which impeded the airplane’s climb performance. Contributing factors were the pilot’s improper preflight inspection and inadequate frost removal procedures.
This case study reinforces the need for pilots to pay close attention to the surfaces of their airfoils and not become complacent in skipping any steps. This unfortunate incident could have ended much worse. Fortunately, the injuries were minor.
How to Perform a Ice/Frost Inspection?
A tactile (touch) test is the best method to confirm there are no frost or ice contaminates on the surface. Depending on the light and the angle of your view, a very thin layer of ice could resemble a wet wing. Therefore, it is especially important to use your hand to confirm that no ice is present and the surfaces are merely wet.
Best Practices to Remove Ice/Frost
If your aircraft has wet snow sitting on top of the airfoils, you can remove it with a soft brush or similar tool. It is important to note that removing ice or hard snow with force, such as trying to break it off, can harm the airfoil. Always gently remove soft snow to get as much of it off the surfaces without using force. Antennas, vents, vortex generators, stall warning indicators, and lights can easily be damaged, so be very careful when inspecting and cleaning their surfaces.
The easiest way to remove frost and snow is to move your aircraft into a heated hangar. Make sure all moisture has been removed from the airfoils prior to moving the plane back outside to avoid any residual freezing.
Some pilots attempt to blow hot air over the surfaces to melt the frost and snow. While this can work, your aircraft’s surfaces are cold, and they typically remain cold. If the water is not completely gone, it will refreeze. This is why hot air is not a preferred method to remove frost and ice.
One of the preferred methods to remove ice from your aircraft is through the use of anti-icing fluid. There are multiple types of anti-icing fluid, but the 2 main factors in deciding which type of anti-icing fluid to use are 1) following your AFM, and 2) knowing your aircraft’s rotation speed. In general, anti-icing fluid is based on aircraft rotation speed.
- Type I is for rotation speeds less than 60 knots. If your AFM does not cover anti-icing fluid and your rotation speed is less than 60 knots, you can use type I. All of the other types discussed below must be approved by an AFM to be used.
- Type III is for aircraft with rotation speeds of 60 knots or more, if approved by your AFM. Types II and IV are for aircraft with rotation speeds of 110 knots or greater and any use of these fluids must be approved by your AFM. The reason these types need approval from your AFM is that they have thickening agents and these agents could cause lifting loss in some aircraft. Further, these agents leave a residue that can rehydrate and refreeze. To be included in your AFM, the aircraft manufacturer must have successfully tested these types of fluids. It’s best to not volunteer yourself to be a test pilot with icing conditions and instead strictly follow all of the guidance in your AFM.
Even If You Can Remove the Ice/Frost from the Airfoils, Can You Fly in Icing Conditions?
GA aircraft will fall within two categories here: aircraft NOT approved for flight into “known icing” conditions and aircraft that are approved for flight into “known icing” conditions. Without having approval for flight in “known icing” conditions, aircraft should avoid weather reported or forecasted to have conditions that would likely cause icing. In other words, avoid or limit exposure to prolonged flight in these conditions. On the other hand, aircraft approved for flight into “known icing” conditions have the ability or equipment to retard icing so they can operate for longer durations in “known icing” conditions. While an aircraft may be certified for “known icing,” as pilots, we must truly understand each onboard system’s role in maintaining the safety of flight and ensure the systems are functioning correctly and as intended. Even with the comfort blanket of a “known-icing” approval wrapped snugly around your aircraft, it does NOT guarantee your aircraft won’t accumulate ice.
What You Should Have Learned
You should ensure by touch that your aircraft’s airfoils do not have ice or frost. If ice or frost is present, it’s best to bring the aircraft into a warm hangar to let the ice melt. Alternatively, you can use anti-icing fluid, but check your AFM to see which type is appropriate for your aircraft. If your AFM does not list an anti-icing agent and your rotation speed is less than 60 knots, you can use Type I. Keep in mind that many aircraft are not certified for known icing. For aircraft certified for known icing, pilots should understand the systems and appreciate that they may not keep ice off of the airfoils in all situations.