No Horizon Over Cook Strait: Trusting Instruments When Your Ears Disagree
You are flying a PA-28-181 single-pilot, night VFR from Paraparaumu to Nelson across Cook Strait. It is a dark night with no moon, no visible horizon and no traffic reported. You climb to 6,500 ft, level off, and reduce power to cruise. Moments later you feel as though you are being tipped forward and to the right, and you have a strong urge to pull back and turn left; your body feels 'heavy' and your inner ears are giving conflicting signals. The attitude indicator shows wings level, the altimeter is steady at 6,500 ft and the ASI reads 108 kt. You have a vacuum-driven AI and a turn coordinator, and no autopilot. You are 12 minutes from the coast-in point, with cloud above 8,000 ft.
1. What is happening to you, and what exactly would you do in the next 30 seconds?
Read the worked answer
This is a somatogravic illusion, probably with a somatogyral component. At level-off the aircraft decelerates, and the otoliths in the inner ear interpret that linear deceleration as a pitch-down or forward tilt. The 'heavy' feeling and the urge to pull back and turn left are the classic result: the pilot follows the sensation, pulls into a climb and can enter a spiral or stall. The attitude indicator, altimeter and airspeed indicator are the reliable references, and they agree with each other: wings level, altitude constant, 108 kt.
In the next 30 seconds: do not act on the sensation. Keep your eyes on the attitude indicator, hold the wings level with small pressures, and set the power and attitude by reference to instruments. Cross-check the altimeter, VSI, ASI, heading and turn coordinator to confirm the AI is not failing. Breathe steadily; the sensation fades once the conflicting motion stops. Only then make a deliberate, small correction. The temptation to 'fix' the feeling with control input is the hazard.
2. Explain why following the sensation would be dangerous in this specific aircraft and flight, and what instrument cross-checks protect you.
Read the worked answer
A PA-28 has a vacuum-driven attitude indicator and no autopilot. If the pilot pulls back and banks left to satisfy the illusion, the aircraft will climb and turn away from the intended track. With no visible horizon and no autopilot, the resulting spiral or stall can progress to loss of control before the pilot recognises it; at night over water, there is no visual cue to recover by. Spatial disorientation is a leading cause of fatal night VFR accidents for exactly this reason.
Protective cross-checks: the AI for attitude; the altimeter and VSI for climb or descent; the ASI for speed trend; the heading indicator and turn coordinator for bank and turn. If the AI is suspected of failing, the turn coordinator, altimeter, ASI and VSI form a partial-panel picture. The discipline is to believe the group of instruments that agree, not the single sensation. In this case the AI, altimeter and ASI all say the aircraft is straight and level, so the sensation is the unreliable source.
3. Once control is regained and the illusion has settled, would you continue to Nelson or divert? Justify your answer.
Read the worked answer
Continuing is defensible only if the pilot is fully reoriented and the workload is manageable. The safer choice is to divert to a lit, controlled aerodrome, most likely Wellington, or to return to Paraparaumu. Reasons: the pilot has just experienced a significant disorienting event, single-pilot, at night, over water, with no autopilot and no visible horizon. The remaining flight to Nelson includes another descent and approach, likely over water in the dark, with a similar illusion risk at level-off and in the turn. Fatigue and adrenaline will also degrade performance after the event.
A practical plan: climb to 7,500 ft in VMC below the cloud, advise ATC of the event, request vectors and flight following, and set a diversion to Wellington. If continuing, brief a stabilised instrument-referenced descent, use the instruments for the entire approach, and set a personal rule that any repeat of the illusion means an immediate go-around and diversion. The decision should be made on risk, not on the inconvenience of a missed appointment.