Introduction
On June 10, 2017, at about 1050 eastern daylight time, a Cessna 172P, registration N881AV, was substantially damaged during an accident at Miami Executive Airport (TMB) in Tamiami, Florida. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight. The flight instructor and student pilot were not injured.
Flight Sequence
Before the flight, the airplane was refueled, and the student pilot took fuel samples, which showed no contaminants. The preflight inspection was completed, and the engine start was normal with gauges in the green range. The airplane taxied from the parking ramp to runway 9L via taxiway Delta without any issues. During the engine run-up, the checklist items were followed, flight controls worked correctly, and the magnetos had two good drops in rpm while carburetor heat showed a normal drop.
The student pilot was asked to demonstrate a soft-field takeoff. He selected 10° of wing flaps, received takeoff clearance, and began the takeoff roll. Engine indications were normal, and airspeed climbed. The student kept the airplane in ground effect to build airspeed, simulating a grass strip or rough field takeoff. At about 80 knots, he climbed out of ground effect and retracted the flaps at 200 feet mean sea level (msl). All indications were normal up to that point.
Accident and Emergency Landing
At about 350 feet msl, the flight instructor heard a slight decrease in power and asked the student if he was guarding the throttle; the student confirmed. The power returned briefly. Then, at about 400 feet msl, the engine lost power again, dropping to 1,900 rpm with fluctuations. The instructor took control, and the power dropped further to 1,100 rpm, continuing to fluctuate. With no runway remaining and losing altitude, the instructor decided to land in a grass field on airport property. Upon touchdown, braking capability was poor, and even with aerodynamic braking, the airplane felt like it was skidding. The left wing struck a tree, then the airplane hit the airport fence before coming to a stop. The pilots shut off everything, including fuel, and egressed.
Wreckage Examination
Examination of the accident site showed the airplane touched down in grass about 200 feet past the end of runway 9L and rolled about 1/4 mile before impacting the tree and fence. The grass was wet due to recent heavy rain, and tire marks were visible from touchdown to the tree. The left wing contacted the tree with the landing and taxi light assembly on the leading edge. The right wingtip fairing was broken from fence impact, and the upper wing skins were wrinkled from the fuel tank filler caps outward to the wingtips. The spinner and propeller were also damaged from fence contact.
Engine Testing
Engine runs were performed after the accident. The cowling was removed, and the engine was completely exposed. Fuel and oil samples showed no contamination and were at appropriate levels. During the first run, the engine operated for 8 minutes: 2 minutes at idle (simulating taxi) and 6 minutes simulating run-up and takeoff, then shut down. A second run lasted 8 minutes. In both runs, the engine ran without hesitation, with no evidence of preimpact mechanical malfunctions or failures that would have prevented normal operation.
Weather and Carburetor Icing Considerations
At 1053, the weather at TMB reported a temperature of 30°C and a dew point of 26°C, yielding a calculated relative humidity of 79%. Review of the carburetor icing probability chart in FAA Special Airworthiness Information Bulletin CE-09-35 indicated that atmospheric conditions were conducive to carburetor icing at glide and cruise engine power settings. FAA Advisory Circular 20-113 recommends that pilots regularly use carburetor heat under conditions conducive to atmospheric icing and apply carburetor heat briefly before takeoff when relative humidity exceeds 50%, especially with float-type carburetors. It also advises remaining alert for induction system icing during takeoff and climb-out when relative humidity is above 50% or visible moisture is present.