Is this correct. Or is there anything else I need to understand about pitot static failures for a commercial ride?

Pitot-static system malfunctions remain one of the most heavily tested and operationally significant failure modes in the commercial pilot curriculum, and the Reddit thread reflects a common study point: correctly diagnosing which instruments are affected based on where the blockage occurs. The pitot-static system feeds three primary instruments—airspeed indicator, altimeter, and vertical speed indicator—and each reacts differently depending on whether the pitot tube, the static port, or both become obstructed. A blocked pitot tube with the drain hole still open causes the airspeed indicator to act like an altimeter, showing decreasing airspeed during climb and increasing airspeed during descent, since only ambient static pressure continues to fluctuate inside the line. If both the pitot tube and its drain hole are blocked, the trapped pressure gets sealed in the line entirely, and the airspeed indicator will behave like an altimeter in reverse—airspeed will rise during a climb and fall during a descent, mimicking a ram-air effect. A blocked static port, by contrast, causes the altimeter to freeze at the altitude where the blockage occurred, the VSI to read zero regardless of actual climb or descent rate, and the airspeed indicator to become unreliable, reading low above the blockage altitude and high below it—the classic "reversal" pilots must recognize.

For working pilots, this isn't purely academic. Pitot-static failures have caused fatal accidents in both general aviation and commercial operations, most notably Aeroperú Flight 603 in 1996 and Birgenair Flight 301 the same year, both traced to obstructed static ports (tape left over maintenance, and insect nests, respectively). Northwest Airlink Flight 5719 and several corporate jet incidents have similarly hinged on pilots failing to cross-check instruments and recognize a static system problem before it cascaded into loss of control. These accidents underscore why the FAA tests this material so rigorously on the commercial and ATP written and oral exams: pitot-static malfunctions are insidious because the erroneous instruments still function and display plausible-looking data, unlike an outright instrument failure with a flag or blank display. The danger is trusting bad information rather than recognizing no information at all.

The practical takeaway for checkride candidates and line pilots alike is memorizing the pattern through logic rather than rote memorization—understanding that airspeed indicator behavior mirrors the source of trapped pressure (pitot blockage reproduces altimeter-like trends, static blockage reproduces reversal errors) makes the system far easier to reconstruct under the stress of an oral exam or, more importantly, in flight. Modern aircraft mitigate much of this risk through pitot heat, alternate static sources, and increasingly through synthetic vision and air data computers that cross-check multiple probes and flag disagreements (as seen in Airbus ADR disagree logic and Boeing's AOA disagree alerts, both partly a response to lessons learned from unreliable airspeed events like Air France 447). Still, examiners expect commercial applicants to diagnose these failures using raw analog logic, since alternate static sources, pitot heat failures, and probe icing remain real-world hazards, particularly in unheated GA aircraft, older business jets, and any airplane operating in icing conditions without functioning anti-ice systems.

Beyond the immediate checkride application, this topic reflects a broader industry emphasis on manual instrument cross-check skills even as cockpits become increasingly automated and glass-paneled. Regulators and training providers have pushed harder on unreliable airspeed and pitot-static scenario training in recurrent simulator sessions for airline and business jet crews precisely because reliance on displayed data without independent verification has proven catastrophic. Whether preparing for a commercial checkride or flying an EFIS-equipped jet at FL410, the underlying skill is the same: recognizing when instrument data is internally inconsistent, understanding the physics behind why, and having a memorized, immediate response—rather than troubleshooting from first principles under pressure. That fundamental knowledge, tested at the commercial level with static diagrams like the one referenced in the post, is designed to build the diagnostic reflexes airline and corporate pilots rely on for the rest of their careers.