Photo from Bundesstelle für Flugunfalluntersuchung (BFU) investigative report
A Special Airworthiness Bulletin was issued in May for the Embraer Phenom 100 ice protection system after a series of incidents involving the formation of ice. The bulletin has no mandated changes but reminds owners, operators and pilots to study the de-icing system and adopt the specific procedures outlined by the manufacturer to avoid undetected ice formation which could result in stalling. It was issued in Brazil and there is currently no airworthiness directive.
The bulletin outlined three separate incidents in three different countries, all relating to the formation of ice and subsequent stalling. The three different incidents outlined similar concerns pertaining to the ice system and are the reason for the bulletin.
Incident One
On Feb 8, 2021, a Phenom 100 took off from Venice, Italy for Le Bourget, France and data revealed the flight crew selected landing speeds for non-icing conditions, in accordance with the normal procedures outlined by manufacturers in the quick reference handbook. Before the plane began its descent to Le Bourget, they were informed about the presence of severe icing between 3,000 and 5,000 feet. The approach was carried out with the normal procedures for an approach in non-icing conditions and the speed selected by the crew was below the approach speed in icing conditions and close to stall speed in the event of ice contamination according to the manufacturer.
The speed was decreased during the final approach, the angle of attack increased from 10 degrees to 28 degrees and the stall warning was activated. Based on the aircraft configuration in this accident, the WINGSTAB de-ice system would have activated the stall warning at 9.5 degrees. The plane stalled with a right bank angle of about 10 degrees and landed hard on the runway, resulting in right and nose landing gear failure.
There was ice found on the wing and stabilizer leading edges during the accident investigation, indicating the deactivation of the de-ice system likely led to the formation of new ice on the aircraft at the end of the approach, or that the built-up ice may not have been completely broken up. The crew had reportedly activated the wing and stabilizer de-ice system for about 21 seconds, which results in a complete de-ice cycle. The crew noted that they had observed the ice broken up on the wing leading edges. They deactivated the system and did not activate it again.
The Bureau d´Enquêtes et d´Analyses pour la sécurité de l´aviation civile (BEA) conducted the investigation and speculated that the light and clouds at the time of the incident did not allow the crew to see the true level of contamination on the wing. Once they deactivated the de-ice system, the crew did not monitor the wing for new formation of ice.
Incident Two
The second outlined incident occurred on Dec. 8, 2014 when a Phenom 100 crashed while on approach to Gaithersburg, Maryland. The NTSB investigation found that the crew had selected the landing speed in accordance with the QRH for non-icing conditions. Pilots reported icing conditions in the clouds with cloud tops from 4,300 to 5,500 feet and the right-seat passenger noted the presence of snow. The investigation found the plane flew for several minutes under conditions favorable for structural icing without the system activated.
During the final approach the plane began to roll to the right and reached a bank angle of about 21 degrees before it began to roll to the left. The plane’s speed decreased and a stall warning was sounded. The plane rolled almost 59 degrees to the left and then went through multiple roll oscillations before it returned to wing level and began another roll to the right.
The plane rolled 100 degrees to the right and then continued to about 154.5 degrees. The plane hit three houses and the ground less than a mile from the approach end of the runway. After the crash, the plane and one of the three houses was involved in a fire.
Incident Three
On Feb. 15, 2013 a Phenom leaving Kortrijk-Welvelgem Airport in Belgium to Berlin-Schönefeld Airport in Germany was involved in an incident. The German Federal Bureau of Aircraft Accident Investigation (BFU) found this crew had selected a landing speed in accordance with the QRH for non-icing conditions. While the plane was beginning its descent, the pilot completed a checklist and chose the landing speeds for non-icing conditions since no visible moisture was detected.
The pilots were given the report, “moderate icing reported below 3,000 ft and cloud base 1,400 ft,” but they only activated the windshield anti-ice and engine anti-ice system for both engines. The plane entered the clouds with just these two systems enabled. The speed decreased on the final approach and the angle of the attack on the left sensor increased to 17.2 degrees. The plane then began a roll left and reached a bank angle of 30 degrees. The left wing suddenly dropped and touched the runway. The Phenom then rolled right and the right main landing gear came down hard. The landing gear was fractured and the plane began to slide along the runway.
The investigation revealed ice at the nose, the entire length of both wing leading edges, the leading edges of the horizontal stabilizer and the front end of the landing gear components after the accident.
Ice formation effects and system
When ice forms it can decrease both the angle of attack in which stall occurs and the maximum lift that the airfoil is capable of, increasing stall speed.
The Phenom ice protection system has a thermal anti-ice system for engine air intakes, an electrical heating system for the windshield and probe and a pneumatic de-ice system for the wing and stabilizer leading edge. The pneumatic system includes inflatable boots, which are activated and inflated for five seconds each minute using engine air bleed, then deflated. This produces cracking and shearing stresses in the ice which causes it to break into pieces and breaks the ice interface with the de-ice surface.
The system has a stall warning “STALL, STALL” which gives the pilots situational awareness if the plane is approaching a stall condition. This also gives a visual cue to the low speed on the airspeed tape for both the primary flight display with red and amber indicators. A stick pusher is activated to prevent a plane from potentially entering a hazardous stall condition.
When the system is activated, the stick pusher and stall warning lower the angle of attack. This protects the plane against the effects of ice formation on the plane. In all three incidents, the crew chose speeds and an approach based on non-icing conditions. The bulletin reiterates the importance of knowing the de-icing system on your plane and its function capabilities and limitations. Limitations are listed in the airplane flight manuals, which all pilots should be aware of in case of ice.
The AFM insists that the de-ice system must be activated when any icing conditions are forecasted. Also, it was previously noted that a minimum ice formation should be present before the boots system is activated, which might not be the case with a modern boots system. The bulletin stresses ensuring no delay in the system activation. It is also essential to make sure that the proper stall and protection system function to prevent a hazardous stall situation.
If there is no ice accretion on the plane, the systems may be turned off, however, the WINGSTAB switch should remain on until the flight crew is sure the entire wing, and unprotected areas, as well as any area behind the de-icing boot are clear from any ice. This is relayed in a specific warning in the AFM.
Recommendations
The recommendations are outlined to keep Phenom 100 owners and pilots flying safely. According to the AFM, the ice protection systems must stay activated in low temperatures and when there is visible moisture. The system may only be deactivated after leaving icing conditions and if the pilot or crew is certain there is no ice formation on the wing or any other part of the plane.
If icing conditions exist or are forecasted, landing and approach speeds should be consistent with a configuration with the ice protection systems activated. The speeds may be adjusted after leaving icing conditions and if the pilot is certain there is no ice formation. The system cannot be turned off to avoid a performance penalty. It is recommended that owners and operators are aware of the Embraer informative video, posted below.
Phenom 100 planes equipped with Garmin 3000 have installed an ice detector as a standard piece of equipment. This is optional for any Phenom 100 equipped with Garmin 1000. The system facilitates an ice condition identification but the pilot is responsible for the activation and deactivation of the system, and knowing the importance of doing so.
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