History of Flight
On 10 May 2006 at 17:35 UTC, a Cessna 172N, registration CS-AZJ, owned by Aeroclube de Bragança, departed from Chaves runway for a leisure flight to Vila Real aerodrome with only the pilot onboard. The flight proceeded at 4500 feet with engine at 2300 RPM (54% power). At ten miles from destination, the pilot had the aerodrome in sight and received clearance from Lisbon Military ACC to contact the Vila Real AITA. Descent from 4500 feet began at eight miles, and the aircraft continued a direct approach to runway 20, situated at 1800 feet altitude.
At three miles, approximately 3500 feet, the pilot reduced engine power and extended 20 degrees of flaps. The descent continued steeply until about half a mile from the runway, when the pilot advanced the throttle and the engine stopped. Surprised but believing he would reach the runway, the pilot instinctively pulled back on the yoke, raised the nose, partially retracted flaps to 10 degrees, and attempted to restart the engine without success. Sensing a rapid descent, which he attributed to downdrafts, and realizing he could not land on the runway, he steered away from trees and prepared for an off-runway landing.
The aircraft came to a stop after about ten meters, sustaining substantial damage from impact with bushes and the aerodrome fence. The pilot exited unaided and was taken to Vila Real hospital, discharged the following day.
Injuries
The pilot sustained minor injuries: abrasions and a small sternum fracture.
Damage
The aircraft sustained substantial damage: cowling dented, left wing leading edge dented, and windshield broken. The aerodrome fence was damaged.
Pilot Information
The 65-year-old male pilot held a PPA license issued by INAC, valid until February 2008. Total flight experience: 1387:25 hours, all in type. Last 90 days: 6:00 hours; last 30 days: 3:00 hours; last 7 days: 0:20 hours. Medical certificate Class 2 with limitation VDL (must wear corrective lenses and have a spare pair).
Aircraft Information
The single-engine, high-wing, fixed tricycle gear Cessna 172N (serial 172 71535, built 1978) was powered by a Lycoming O-320-H2AD engine (160 HP) and a McCauley fixed-pitch propeller. Total airframe hours: 3028:45; hours since overhaul: 11:55 (engine 11:05). Last inspection: 4 February 2006. The aircraft had a valid navigation certificate and complied with the maintenance schedule.
Meteorological Information
Synoptic chart at 17:45 on 10 May 2006: 1/8 cumulus at 1500 feet, 3/8 cirrus at 20000 feet; wind 290/08 knots; temperature 23°C; dew point 8.5°C.
Examination and Research
Technical inspection of the engine at Industrias Aeronáuticas de Coimbra found no anomalies in fuel, ignition, lubrication, or other systems. The investigator considered carburetor icing as a probable cause of the engine stoppage. Carburetor ice can form at temperatures up to 37.8°C and relative humidity above 50%, most frequently between 0°C and 21.1°C with humidity above 80%. Precautions include periodic checks of carburetor heat and applying it before takeoff in high humidity, and periodically advancing the throttle during prolonged descents with reduced power.
Probable Cause
Carburetor icing was considered a probable cause of the engine stoppage.