Several years ago, a fatal mishap occurred in a Beech Duke at Wilmington, Delaware. The failure that instigated the crash would be very hard to correctly identify in real-time from the pilot’s seat. As multiengine pilots, we’re trained to respond to the indications this failure would present in exactly the wrong way. In a single-engine turboprop, the condition might surprise us as well.
From the NTSB (Accident Number NYC08FA051):
“According to a witness, prior to arriving in the run-up area, the pilot lowered the airplane’s flaps. After the right flap fully extended, the flap key on the drive shaft inside the 90-degree drive assembly adapter fractured, in overload, in the direction of flap extension. Before takeoff, the pilot raised the flaps; however, with the fractured key, the right flap would have remained fully extended. The pilot could not have identified this condition prior to takeoff, either visually [because of the Duke’s window design] or by means of the flap indicator, which received its input from the right flap actuator.
“The pilot subsequently took off, and the airplane turned left, but it is unknown at what point the pilot would have noted a control problem. The pilot climbed the airplane to 250 to 300 feet and allowed the airspeed to bleed off to where the airplane stalled and subsequently spun into the ground. Airplane manufacturer calculations revealed that the pilot should have been able to maintain control of the airplane at airspeeds over 70 knots. According to the pilot’s operating handbook, the best two-engine angle of climb airspeed was 99 knots, and the best two-engine rate of climb airspeed was 120 knots.
“The National Transportation Safety Board determines the probable cause(s) of this accident to be: The pilot’s failure to maintain adequate airspeed during a split flap takeoff, which resulted in an aerodynamic stall. Contributing to the accident were the failure of the right flap drive mechanism and the pilot’s failure to verify that both flaps were retracted prior to takeoff.”
Preconceived failure
Put yourself in the pilot’s seat. After completing the Before Takeoff checklist and any line-up final items you include in your regimen, you advance both throttles smoothly to the forward stops. You confirm manifold pressure, RPM, fuel flow, and oil pressure are as expected for both engines. You crosscheck that the exhaust gas temperatures (EGTs) and, if turbocharged, turbine inlet temperatures (TITs) meet your targets or adjust the mixtures as needed if they don’t. At “rotation” speed (in those POHs that use this term) or a few knots before “liftoff” speed (for those using this instead), you apply back pressure to bring the airplane to the initial climb attitude. The wheels kiss the pavement goodbye; positive rate, gear up.
But you’ve had the same flap failure as that Duke pilot. The left flap is up, but the right flap is fully down. In the blast behind the propeller running at full power, the added lift on the right side creates a dramatic roll to the left. You’re a well-trained piston twin pilot—what does all your training tell you is happening when the airplane suddenly rolls to the left immediately after takeoff? That’s correct; you know it’s a failure of the left engine. It’s what we train for.
You push the nose down to attain and maintain VYSE, “blue line” speed.” You step down hard on the right rudder to stop the yaw and hold heading. This is the correct response, whether this is an engine failure immediately after liftoff or a split-flap takeoff. So far, so good. Here’s where your response needs to slow down to meet the realities of the emergency. If you act rashly, you might reach up, grab the left propeller control and pull it back into feather. I’ve seen this done many times as a Baron simulator instructor—the pilot is convinced they know the problem because instructors have drilled this response into them their entire multi-engine life. They feel the need to act right now to feather the “dead” engine’s propeller.
Except…if the problem was an extended right flap instead of a failed left engine, feathering the propeller would create even more disparity between lift on the right side and lift on the left. The airplane would roll even harder to the left. The scenario would probably be over as rapidly as it was for that unfortunate Duke pilot.
Swift, but methodical
If instead, you follow the engine failure “drill” as intended, you’ll do several things before you yank the prop control into feather. Identify the failed engine using control feel, i.e., “dead foot, dead engine.” The split flap scenario gives you no clues here; it still suggests your conditioned response. Verify by pulling the suspected dead engine’s throttle back substantially. Here’s where you must slow down—pull the throttle back halfway or more and evaluate control feel again. If pulling the throttle requires you to change your rudder input to hold heading, then either:
- you’ve misidentified the failed engine;
- you’ve selected the wrong throttle control for the engine you’ve identified; or
- you don’t have a dead engine, after all.
Reducing throttle and getting a change in control feel might be very confusing because it contradicts what all your training tells you to expect. But pausing long enough to confirm your suspicions can save your life. Where else might you look? If the EGTs/TITs are on target, then the engines are running as expected. The exhaust gases’ temperature will plunge immediately after failure, giving you near-instantaneous confirmation of whether and which engine has failed. One last check: assuming the throttle verification step confirms a dead engine, verify one more time with the propeller control. Instead of snatching it immediately into feather, pull it partway back and confirm once again there’s no change in rudder requirement to hold heading. If you’ve positively verified this a second time, then pull the control into feather. I’ve seen pilots get past throttle verification in the Baron simulator and even active airline pilots in a Piper Seminole simulator when I was a consultant to Embry Riddle, only to grab the wrong propeller control and feather.
When you suspect a failed engine, it’s far more important to be correct than to be quick. Complete the engine failure “drill” swiftly but, more importantly, methodically…evaluating the airplane’s response with each completed checklist step.
Fixing asymmetry
If you confirm both engines are still running, what do you do? Simple: fly the airplane. Hold optimal performance speeds and accept what performance the airplane will give you until you resolve the situation, usually by safely putting the airplane on the ground for deeper investigation.
If you’ve positively determined (by visual check) that you have an asymmetric flap extension, you may be able to remove the asymmetry—that’s where your systems knowledge comes in. Most Pilot’s Operating Handbooks and Airplane Flight Manuals (POH/AFM) contain no guidance on responding to an asymmetric flap extension. But for many airplane types this technique should work. Once established at a safe speed and altitude with no difficulty maintaining control:
- Ensure the FLAP MOTOR circuit breaker is in.
- Extend the UP flap, if possible, to match the position of the other flap.
- Retract the DOWN flap, if possible, to match the position of the other flap.
- If one flap is stuck in an intermediate position, use the switch to extend or retract one flap to match the position of the other.
- Pull the FLAP MOTOR circuit breaker when the flap extension is approximately the same on both sides.
- Land with flaps in the matched position.
If you’re unable to match flap positions, select the longest available runway with the lowest possible crosswind, and keep your speed up to touchdown to retain control
Other lessons
The Duke pilot apparently included a Before Takeoff checklist procedure I’ve seen performed by many pilots and even taught myself when I was instructing at Beech Field back in the 1990s: run the flaps through every position to confirm the indicators and limit switches are working properly. In airplanes with the approach flap preselect, this means moving the handle from Up to Approach, confirming the flaps stop halfway out, going from there to full Down, afterward raising the flaps again to Approach, and then bringing the flaps fully Up—pausing each time to confirm the flap goes to the selected position and the flap motor stops.
The trouble is, in many types, it’s difficult or even impossible to see the right flap from the left seat (such as in the Duke). But is this flap check really necessary just before takeoff? It’s my opinion that we should not check the flap operation on the Before Takeoff checklist. Check full operation of the flaps during scheduled inspection and when accepting the airplane from maintenance while it’s in the hangar. Occasionally check flap operation as part of your preflight inspection, so you’ll see a split flap condition before you try to fly. Assure the flaps are set for takeoff before you get back into the airplane, then leave them alone before takeoff. If you experience what feels like an engine failure shortly after takeoff, be swift but methodical in your response to avoid misidentifying what might be a completely different type of emergency.
