What’s In Your Landing Calculus? ASAP #34781, KC-135 Aircraft Experiences Difficulty Slowing Down on Wet Runway, Stops on Overrun

We recently received an excellent ASAP, which gives us a scenario to explore the question: What’s in your landing calculus? In other words, what are your landing considerations when deciding whether to land or go around?

A landing decision is situationally based; thus, it is a dynamic assessment that can only be made at the time of landing. However, you can have a predetermined set of factors that you examine when making your landing or go-around decision. This article will not be all-encompassing, but hopefully, it will get you to think about your own landing criteria and decision-making process. To help shape our thoughts, we will organize our landing criteria under the major labels of environmental factors, aircraft factors, and procedures.

As we go through this ASAP analysis, you should focus on the factors that shape your decision-making process. It is very easy to sit back in a nice, comfy chair at “ground speed zero” and be critical of the ASAP crew’s decision-making. Hindsight is always 20/20 when the outcome is known. If you are judgmental of the crew’s decision, then you are missing the point. No two landing decisions are identical; thus, we should analyze factors that shape our decision-making process. Finally, this ASAP was submitted anonymously; therefore, we were unable to contact the crew for additional information and answers. The analysis presented is based on known data sources without the crew’s input. We do not know what information was positively known to the crew, nor what data sources were used by the crew.

ASAP #34781 Event Narrative

Flying into [BASE]. wet conditions. KC-135 Left seat pilot flying and was 5-10 knots fast but inside the safety margins. crossed threshold 70 feet so 20 feet high but landed in the zone. All wheels on the ground before 7,000 remaining. computed ground roll 6,740. VB109. Aircraft was not decelerating at 5,000ft remaining. PF got on the brakes 125kts. Brakes were not effective. Aircraft was hydroplaning. 2,000 ft remaining and 70-80 knots. PF asked Rt seat PM to try brakes to see if it was problem with with Lt side brakes. PM brakes ineffective. Aircraft came to a stop a plane length into the overrun. It was a paved over run. Lessons learned. Query the tower about Rwy condition in search of standing water conditions. A firmer landing would have helped break through water level and potentially eliminated some of the hydroplaning.

ASAP #34781 Submitter’s Suggestions

Query the tower about Rwy condition in search of standing water conditions. A firmer landing would have helped break through water level and potentially eliminated some of the hydroplaning. check if rwy grooved or not and treat wet conditions like ice if not grooved.

Environmental Factors

In this ASAP event, there were two important environmental considerations: airfield and weather.

The runway is the obvious airfield factor that always plays a role in our landing decision. Of course, runway factors, such as length, width, and weight-bearing capacity, are common considerations for determining whether we are legal to land on certain runways; however, a multitude of other factors may be worthy of landing considerations. During pre-mission planning, we can pull airfield data from plenty of approved sources, such as the Instrument Flight Rules (IFR) Supplement, Area Planning series, the Airfield Suitability and Restrictions Report, and the Airfield Detail (Giant Report).

In the case of ASAP #34781, the runway data seemed straightforward and approved for KC-135 operations; however, there were some important notes in the remarks section. Note: The aircraft landed on 3R.

Upon careful study of the REMARKS section of the airfield data, which is shown in the excerpts, you will see two important data points. The first data point is a caution regarding hydroplaning. The second data point is an actual description of runway grooving for both runways. Similarly, you will find data points highlighting standing water, the risk of hydroplaning, and runway grooving contained in the Restrictions and Remarks of the Giant Report.

These two remarks are provisional based upon weather conditions. Of course, during pre-mission planning, we cannot accurately depict actual weather conditions upon our landing. Part of pre-mission planning is building situational awareness of the environment, anticipating threats, and planning how to mitigate those threats in the future. So, although we may be comfortable with ten thousand feet of runway on a clear, dry day (low risk), the risk may increase if weather conditions change our landing calculus.

The ASAP narrative highlighted weather as a factor in the event. According to Meteorological Aerodrome Report (METAR) observations, airfield management logs, and air traffic tower logs, light rain was noted during each weather observation approximately four hours before the event. Additionally, before the KC-135 crew landing, the last reported braking action was medium, which was reported by an F-35. This report was passed to the KC-135 crew before landing.

The Aircraft Factors

The aircraft we operate plays a critical role in our landing decision-making process. We spend an enormous amount of time studying and understanding aircraft performance, restrictions, limitations, and procedures, especially in the approach and landing phase of flight; however, we should not become complacent in our analysis of aircraft considerations and how they influence our landing decision.

In the case of ASAP #34781, the event begins to highlight the complexity of the aircraft considerations given the possibility of hydroplaning, a non-grooved runway, runway conditions based on the light rainfall. According to T.O. 1C-135(K)R(II)-1, Section VII: Adverse Weather Operations, viscous hydroplaning is possible during light rain on a wet runway that is not grooved.

During our ASAP analysis, we ran two KC-135 Takeoff and Landing Data (TOLD) calculations based on a runway condition reading (RCR) value of nine (wet) and an RCR of six (ice) to approximate landing performance. The landing distance based on an RCR value of nine is approximately eight thousand feet. In comparison, the landing distance based on an RCR value of six is approximately nine thousand feet. The two TOLD calculations highlight how a change in RCR value can increase landing distance by approximately one thousand feet. More importantly, these TOLD calculations help us understand the energy management discussion later in the article.

ASAP #34781 Stable Approach Analysis

According to the Military Flight Operations Quality Assurance (MFOQA) analysis of the ASAP event, based on the ground track of the aircraft, the crew most likely flew a visual 50 flap approach, which concluded with a left base for runway 3R. At both one thousand feet and five hundred feet height above aerodrome (HAA), the aircraft was twenty-seven knots above approach speed. At five hundred feet, the aircraft was outside of stable approach parameters due to airspeed; therefore, the crew should have executed a go-around.

The aircraft crossed the runway threshold approximately twenty-nine knots above threshold speed. MFOQA analysis also showed the final power pull to idle occurred at approximately  thirty feet HAA. Based on the gross weight of approximately 177,000 pounds and increased airspeed, the power pull occurred late. Subsequently, the aircraft touched down fourteen knots too fast, approximately thirty-eight hundred feet down the runway, leaving approximately sixty-two hundred feet of runway remaining.

In reference to the statement in ASAP submitter’s recommendation that “a firmer landing would have helped break through water level and potentially eliminated some of the hydroplaning,” the MFOQA analysis indicated the vertical acceleration at touchdown to be 1.03 G. In comparison, MFOQA analysis from the past year showed that KC-135s with a landing weight of 175,000 to 185,000 pounds typically registered 1.17 G at touchdown. Conversely, only five percent of landings had a G spike of 0.95 to 1.05 G. During landing rollout, the speed brake deployment occurred approximately six seconds after landing, consistent with the fleet-wide trend of seven to nine seconds after landing. Finally, the initial brake application occurred at approximately 126 knots.

Stable Approach Criteria—The Why

The stable-approach criteria are a critical tool in the landing decision process. When we execute the approach, the stable-approach criteria become a tool in measuring energy management and its risk.

The physics of flying an aircraft can be simplified to proper energy management. A successful landing boils down to dissipating the proper amount of energy to set the aircraft down and stop it on the runway. The stable-approach point seeks to define a point in space where the aircraft is at the correct energy state, increasing the probability of a successful landing (conversely reducing the risk of an unsuccessful outcome). During the approach phase, we should have multiple checkpoints or gates where we assess our energy state and correct for deviations, as necessary. Energy management is how we handle our energy to put the aircraft where we want it at the correct space and time. Therefore, stable-approach criteria should be a forcing function to plan and define that point in space at which we are confident that we have dissipated the right amount of energy to land the aircraft successfully.

Furthermore, the stable-approach point should not be our only decision point. A stable approach does not guarantee a successful landing. You could fly a beautiful, precise approach, have a late-power reduction, and float down the runway, putting you outside your intended landing zone. Our Air Force Tactics, Techniques, and Procedures publications emphasize defining the latest touchdown point. This clearly defined point, commensurate with our landing calculations, should be the final decision point for assessing risk and directing action (land or go around). These procedures and techniques are all focused on energy management (“how goes it”), defining a decision point, and directing action.

In the case of ASAP #34781, the combination of stable approach analysis and TOLD calculations helps us better understand the energy management scenario. First, the MFOQA analysis highlights that the aircraft was twenty-seven knots above approach speed at five hundred feet. Subsequently, crossing the runway threshold, the aircraft was approximately twenty-nine knots above threshold speed and fourteen knots fast at touchdown. Simply put, the aircraft had excess energy, which had to be dissipated in the air or on the ground (during braking).

Looking back at the TOLD calculations, T.O. 1C-135(K)R-1-1 highlights that speed deviations change the landing performance calculations; thus, the combination of excess speed and late power reduction resulted in a long landing. The increased risk was further amplified due to the potential for hydroplaning, resulting in a longer stopping distance.

Implementing Your Landing Calculus

Deliberate Planning Leads to Better Decisions

The more landing factors we can anticipate and analyze, the more we improve the odds of a good decision. Likewise, the more we can plan at “groundspeed zero” in the flight planning room, the more we can reduce the risk of mission pressure or rushing, which can negatively influence our decision. Although we obviously cannot make our landing decision during pre-mission planning, we can build situational awareness for the landing and assess the risk factors.

Execution Planning—How to Utilize Briefing Procedures

As we move to execution planning (in the aircraft), we should have a good grasp of the situation. If our pre-mission planning was effective, our execution planning should update our pre-mission plan; however, we need to be deliberate in our execution planning to ensure we are systematic and accurate in our review.

Our published briefing guides do an excellent job of stepping us through the planning process by identifying hazards, risks, and mitigation strategies. Additionally, these guides help us communicate and coordinate decision points, division of tasks, and execute decisions and callouts. Most of the factors in our landing calculus are included in our briefing items. Utilize the briefing guides to effectively plan your approach and landing.

As the briefing guides highlight, ensure you have clearly defined your critical decision points, including your stabilized approach points and criteria and your earliest and latest touchdown points. Those decision points should be predicated on the expected aircraft configuration, environmental conditions, and accurate performance calculations. Those critical decision points should be coordinated with crew members and communicated through standardized callouts.