History of the Flight
On 30 January 2020, a Cessna 310R registered N443LT departed from Toussus-le-Noble aerodrome at 12:14 local time for an instrument flight rules (IFR) training flight to Pontoise Cormeilles-en-Vexin. The flight was intended to familiarize the pilot receiving instruction with the aircraft. The control tower cleared the aircraft to 3,000 ft. Between 12:17 and 12:20, while in contact with the south departure controller at Paris-Charles de Gaulle Airport, the aircraft's altitude fluctuated between 3,350 ft and 2,650 ft. The controller requested the pilot to maintain 3,000 ft, and the instructor acknowledged, stating they were flying manually.
Shortly after being asked to switch to the Pontoise frequency, a Minimum Safe Altitude Warning (MSAW) appeared on the controller's radar screen. The aircraft descended to 600 ft with a calculated mean vertical speed of approximately -4,800 ft/min. The Paris-CDG controller attempted to contact the pilots; the instructor reported a minor problem and that they were climbing again. The controller offered assistance, which was declined. The aircraft then climbed rapidly back to 3,000 ft and continued to Pontoise, where the pilot made two IFR approaches before returning to Toussus-le-Noble, landing at 13:18.
Additional Information
Meteorological Conditions
A SIGWX chart forecast a cloud ceiling between 200 and 1,000 ft in the Paris region. WINTEM data indicated southwesterly winds of 35 kt at FL20 and 30 kt at FL50. Radiosonde measurements at Trappes showed a west-southwesterly wind of 35 kt at around 3,000 ft. METAR reports from nearby aerodromes indicated a cloud ceiling at approximately 900 ft with south-southwesterly winds of 5 to 12 kt. The pilots reported flying in cloud with broken to overcast conditions, but had visual contact with the ground during the recovery.
Flight Path Analysis
Between 12:20:17 and 12:20:45, the aircraft descended 2,250 ft, from 3,300 ft to 1,050 ft, against an assigned altitude of 3,000 ft. The mean vertical speed was about -4,800 ft/min, and the maximum recorded descent rate was -9,581 ft/min. At its lowest point, the aircraft was 6 km north of Beynes aerodrome, near an antenna at 909 ft. Between 12:20:49 and 12:21:28, it climbed to 3,150 ft at a mean rate of +3,200 ft/min. Ground speed increased significantly, reaching a maximum of 249 kt at 12:20:53, compared to a mean of 143 kt in the preceding three minutes. The BEA noted that radar-derived speeds may be inaccurate during dynamic maneuvers.
Pilot Information
The 34-year-old instructor held an ATPL(A) license with multi-engine and instrument ratings, plus instructor and examiner certifications. He had about 6,100 flight hours, including 2,700 as an instructor. The 36-year-old pilot receiving training held a CPL(A) issued in April 2019 with multi-engine and instrument ratings, logging about 250 total hours, 108 as pilot-in-command, and 20 IFR hours. He had not flown since obtaining his license and had completed about 50 hours on a B737 simulator.
Pilot Statements
The pilot reported being surprised by the control heaviness from rotation and struggled with elevator trim. He initially used manual trim but had difficulty stabilizing the aircraft. Before the altitude loss, he used the electric trim control, making an excessive nose-down input combined with nose-down stick. When he attempted to stop the descent, controls felt very heavy. The instructor took over during the pull-up and used the electric trim on his side. Neither pilot perceived the high vertical speeds or unusual bank angles. The instructor noted the pilot was intimidated by the heavy controls.
Aircraft Information
N443LT was a twin-engine Cessna 310R with 285 hp engines. It had classic instrumentation and an autopilot. The VNE was 223 kt, VNO 181 kt. The elevator trim had both electric (dual rocker switch on left seat stick) and mechanical controls. No anomalies were reported post-flight by a co-owner.
Conclusions
The BEA concluded that the scenario involved a loss of altitude during an instructional flight, with the pilot struggling to stabilize the aircraft and making an excessive trim input. The instructor recovered control. No probable cause was assigned.