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Ep 32 – Ground Proximity Warning Disabled

Podcast | October 6, 2022

Do you duck under the slope? I sure have. Have I intentionally landed long? Sure have. I landed very long at ATC’s request in Moses Lake to get out of the way of a 747 doing touch-and-goes for Japan Airlines. I’m not saying it’s wrong, but there is a level of risk involved. If your procedures say you should land in the touchdown zone, then that’s where you should land.


In today’s podcast, I’ll be reviewing an accident where no one was hurt, thankfully. However, the crew decided to duck under the slope, landed short of the runway and destroyed the aircraft.


The First Officer offered to disable the Enhanced Ground Proximity Warning System (EGPWS) with no prompting from the Captain, who agreed. It appears there was a tendency at this operator to duck under the slope and perhaps disable the protection offered by the EGPWS. The occurrence happened in August of 2019 when a Cessna 560XLS crashed while attempting to land at Aarhus, Denmark. The aircraft struck an ILS antenna and then touched down before the runway. The weather was night IMC, although the crew could see the runway in time to visually fly to the threshold. In an attempt to land and stop as quickly as possible due to a perceived risk of low visibility in fog over the centre of the runway, the aircraft struck the ground well before the paved surface. The nose gear collapsed on the landing roll in the grass, and a fuel tank was punctured and a fire started when the aircraft came to a stop on the runway. Luckily, none of the 3 crew and 7 passengers were injured. The aircraft was a total loss.


In the preflight briefing, the crew decided not to descend below 17,000 feet if the weather was below minimums at Aarhus. The weather was above Category 1 minima with RVRs at 3,000/2,300/1,300 feet with fog patches and 200 few. The First Officer erroneously told the Captain the visibility was 2,500 meters when, in fact, it was 250 meters. The Captain briefed the ILS, and a clearance was received for the ILS 10 right. With the autopilot engaged and at 2,000 feet, the aircraft started to descend on the glideslope (GS). The Captain called visual contact with the approach lighting system through shallow fog. The First Officer also reported seeing the lights. The gear was selected down, and approach flap was set. The aircraft was configured and cleared to land with wind calm.


At 1,500 feet, the aircraft was on the GS. At 900 feet, the Captain disconnected the autopilot and said, “Runway in sight.” He then said he was going to touch down right at the threshold to avoid the fog in the middle of the runway. He began to fly one dot low on the GS but did communicate this to the FO. Trending lower on the GS, the First Officer asked if the Captain wanted the EGPWS disabled. The Captain agreed, and the EGPWS was disabled at 500 feet AGL. The Captain noted that the PAPI was three red lights and one white. The aircraft announced minimums with full-scale GS deviation and, at this point, the thrust levers were reduced to idle.


The Captain called “Continue,” and the First Officer said that he felt the Captain had sufficient visual reference to continue the approach and landing. There were no calls made regarding the GS deviation. Once closer to the ground, lights were visible, but which lights were interpreted as indicating the beginning of the runway was unclear. The Captain believed he had crossed the runway threshold and initiated a flare. The aircraft immediately struck the ILS antennae for the opposite runway end, which is located 1,500 feet from the threshold. More antennae, light stands, and infrastructure were hit as the aircraft travelled over the grass. A wing fuel tank was punctured. The nose gear collapsed as it struck an object. The aircraft rolled through the stopway and onto the landing surface, where it came to rest 230 meters from the beginning of the paved surface.


The Tower could not see the aircraft and was unaware of any occurrence until the First Officer said on Tower frequency, “Tower, Delta Whiskey Mike, we had a crash landing.” The Tower responded, “Say again,” but no response was heard. The term MAYDAY was never used. Crash fire rescue services were alerted.


After the aircraft came to a stop, the cabin crew initiated an evacuation after seeing the fuel ignite. The pilots did not tell the cabin to evacuate, nor was an announcement made. The First Officer entered the empty cabin and felt the heat of the fire and told the Captain. The pilots evacuated to the location of the passengers and cabin crew. The fire destroyed the aircraft.

In The News: Making Clean Jet Fuel out of Carbon Dioxide Emissions

Let’s change gears for a moment. In The News is a section of the podcast where I talk about other happenings in aviation.


Most Sustainable Aviation Fuel (SAF) is made out of feedstocks such as forestry and agricultural waste, used cooking oil and more, but there is a company in California called Twelve that is making SAF out of carbon dioxide. Twelve is quoted as saying:

“Our process takes CO2, water and electricity as inputs. We use the electricity to break apart CO2 and water, and then we have catalysts that recombine the elements to make new products. And one of the things that we can make is the building blocks for jet fuel.”


The company says that this process is much cheaper than current SAF production techniques because the related costs of CO2 capture have also fallen. The company uses an electrolyzer system that uses electricity to break CO2 and water into the components of jet fuel. As with other types of SAF, the aircraft does not require modification. Microsoft and some U.S. airlines are investors in the company.

Report Findings

Ok back to the podcast. Some of the findings from the final report include the following:

  • The licenses and qualifications held by the flight crew, flight and duty times, the pre-flight planning phase, the documented technical status of the aircraft, the aircraft weight and balance, issued NOTAMs, chart presentations, the status of navigation aids, and the status of the CAT 1 approach and runway lighting system had no influence on the sequence of events.
  • The forecasted weather conditions at the destination were generally consistent with the actual weather reports.
  • The First Officer perceived, noted, and read back to the Commander the meteorological visibility to be 2,500 meters instead of the reported 250 meters.
  • The reported controlling RVR values were above the applicable CAT 1 approach minima and did not prevent the flight crew from performing the ILS approach for runway 10R.
  • From an operational point of view, the Commander’s concern about entering fog patches during the landing roll was unjustified.
  • Appropriate risk controls like the EGPWS (with alerts for excessive GS deviations) and SOP on callouts and stabilized approach were in place at the operator.
  • Before leaving 2,000 feet on the GS, the flight crew obtained visual contact with the approach and runway lighting system for runway 10R. Passing approximately 1,500 feet, the flight crew agreed on visual contact with the approach and runway lighting system, fog above the middle of the runway, and that the touchdown zone and the runway end were both visible.
  • At approximately 900 feet, the Commander disengaged the autopilot.
  • The Commander communicated his intention of landing in the beginning of the runway but not his action plan. The First Officer did not challenge the intention of the Commander. The action plan of the Commander was to fly one dot below the GS and touching down on the threshold, which required initiation of the flare when passing above the stopway for runway 28L. The Commander started flying below the GS.
  • Both pilots accepted and instituted a deactivation of a hardware safety barrier by cancelling potential EGPWS GS alerts for excessive deviations.
  • The First Officer seemed to be familiar with the non-standard procedure on flying below the GS.
  • Passing 500 feet, the aircraft was still within the operator criteria for a stabilized approach. Passing the set ILS approach minima, the aircraft was flying more than 2 dots below the GS and was no longer within the operator criteria for a stabilized approach.
  • The First Officer as pilot monitoring believed that the Commander, by calling “Continue,” had appropriate visual cues to complete the approach and landing. At low altitude, the First Officer made no corrective callouts on altitude, GS deviation, or unstabilized approach.
  • The Commander noted the availability of the PAPI as a visual cue (one white and three red lights).
  • The First Officer, in a critical stage of the flight, did not provide effective monitoring and operational support to the Commander and did not recognize the unstable approach.
  • The crew could see over the nose of the aircraft at 58 feet when the flare was initiated. The Commander most likely mixed up the two red omnidirectional aerodrome fence obstacle lights with the stopway red edge lights to runway 28L and also misinterpreted the CAT 1 approach and runway lighting system for runway 10R.
  • A touchdown on soft but solid ground in a landing attitude at low airspeed absorbed most of the impact forces and reduced the risk of serious injuries to passengers and crew.
  • The flight crew and the cabin crewmember did not coordinate the aircraft evacuation process, although it was effective.
  • The Commander’s rank and experience at the operator might have biased the First Officer on final approach to allow concentration of power in one person steepening the authority gradient.
  • A visual illusion might have provoked a steeper-than-intended short final approach and target fixation on touching down on the threshold, leaving out alternate options like aborting the approach.

The report summarized the factors of the occurrence as follows:

  1. Deviations from SOP in dark night and low visibility combined with the cancellation of a hardware safety barrier compromised flight safety.
  2. The commander started flying below the GS.
  3. Both pilots accepted and instituted a deactivation of a hardware safety barrier by cancelling potential EGPWS GS alerts for excessive GS deviations.
  4. Both pilots accepted and instituted a deviation from SOP by not maintaining the GS upon runway visual references in sight.
  5. At low altitude, the first officer made no corrective callouts on altitude, GS deviation or unstabilized approach.
  6. The confusion over and misinterpretation of the CAT 1 approach and runway lighting system resulted in a too-early flare and, consequently, a CFIT.

No safety recommendations were issued.


Ground Proximity systems can be different across aircraft types. The 737 has options as to which warnings related to the GPWS you can inhibit. Our version does not have Runway Awareness and Advisory System (RAAS), so the runway inhibit switch is not installed; however, flap, gear and terrain inhibit are. Each can be used in different or the same scenarios such as flap inhibit for a single-engine approach and landing, gear inhibit for ditching or partial gear extension landing, and terrain inhibit also for ditching. The only time terrain inhibit is used in the checklist is for ditching.

Have a look at your manuals, and review your approach and landing criteria.

Thanks for listening, and have a great day!


Accident Investigation Board Denmark. (June 2020). Report 2019-327.


Olick, D. (August 20222). Microsoft and Alaska Airlines are working with this startup to make clean jet fuel from carbon emissions. CNBC.


SKYbrary. C56X, Aarhus Denmark, 2019.

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