Human Factors Incident Reporting — Page 326, Lesson 532

I want to walk you through a real-world incident report that illustrates how human factors can degrade flight safety, even when the pilots are experienced and the aircraft is serviceable. This is from the Human Factors Incident Reporting chapter, and it describes a specific event at Heathrow. Let me set the scene. During the taxi out, there seemed to be a problem. It's likely that the warning light on the stick pusher system kept illuminating as the aircraft bounced over the ridges in the taxiway. The stick pusher system is a stall-protection device — if the aircraft approaches a stall, it physically pushes the control column forward to lower the nose and increase airspeed. So a warning light from that system is a significant indication. Because of this distraction, the line-up of the aircraft on the runway was delayed. Eventually, though, the decision was made to line up and take off. The take-off run itself was normal. Rotation — that's the action of raising the nose for take-off — occurred at 139 knots. Unstick, the moment the wheels leave the ground, was at 145 knots. The landing gear was almost immediately retracted, and the V2 safety speed — that's the minimum safe climb speed with one engine failed, also called the single-engine safety speed — was passed at 152 knots. At 170 knots the autopilot was engaged. Now here's a key error: slightly the wrong speed was set in the autopilot box. It should actually have been 177 knots, but even at this reduced climb speed there was still a safety margin, although it was somewhat reduced. The captain, Captain Key, was described as a stickler for procedures. However, it was noted that the autopilot was engaged very early, and Key's radio transmissions were terse and non-standard — meaning short, abrupt, and not following proper phraseology. That's a red flag for stress or frustration. Ninety seconds after commencing the take-off run was noise abatement time. Noise abatement is a procedure to reduce aircraft noise for people living near the airport — in this case, residents local to Heathrow. This required the pilots to throttle back the engines. At this point the engines were throttled back as required. The flaps were also retracted, as was normal. Now, because of three factors working together — the reduced thrust from the engines, a turbulent day, and an incorrect target speed being set in the autopilot — the aircraft was having difficulty maintaining its speed in the climb. At times the climb speed dropped to about 157 knots, which was 20 knots below target. No one seemed to notice. The report suggests that this was a result of the combination of Key's general attitude and his specific demeanour as a result of this outburst, and the other pilot, Keighly's quiet, retiring nature and his general lack of confidence. You can see how the captain's stress and non-standard behaviour, combined with the first officer's reluctance to speak up, created a situation where a significant speed deviation went uncorrected. Let me show you a diagram that illustrates the stall and deep stall concepts relevant to this scenario. This shows the stall condition. And here's the critical one: This shows a deep stall, where the aircraft is uncontrollable and irrecoverable. That's the ultimate danger when you lose speed awareness in the climb — you can enter a regime from which there's no recovery. This incident is a classic example of how human factors — stress, poor communication, procedural deviations, and the failure to monitor — can erode safety margins even when the aircraft is performing normally. The technical details of speeds and systems are important, but the real lesson here is about the human element.