PILOT TECHNIQUES

When go-around is impossible-defining the point of no return

Total preparedness and full briefing can avoid risky last-second decisions.

By Nihad Daidzic .ATP/CFII.
and Thomas Peterson. ATP. Boeing 747, 757, 767


Tropical storm over OPF (Opa-Locka, Miami FL). Landing on a contaminated runway may lead to an impossible situation where an overrun is certain, but no safe go-around is possible either.

A small corporate jet touches down 2500 ft from the threshold of a wet 5500-ft runway with 15 kts excess airspeed. On touchdown, the crew manually extend ground spoilers/lift-dump and deploy thrust reversers while smoothly lowering the nose gear.

Subsequently, they increase thrust to provide for maximum retarding force. The captain pushes on the brakes and the antiskid system works flawlessly, modulating the oil pressure to deliver the maximum braking efficiency while preventing the wheels from locking.

Within moments the crew realize that something is wrong. The aircraft is not slowing down as expected. Only 2000 ft of the runway remain and they are still rolling at well over 115 kts. The captain asks the FO to check the lift-dump deployment and verify the thrust reverser setting.

The captain pushes harder on the brakes. Only 1000 ft of runway remain and the jet has barely slowed to 100 kts. Realizing that they cannot stop on the remaining runway and fearing an overrun and aircraft damage, the captain calls frantically for a go-around.

He throttles back and restows the reverser. Spoilers are retracted. The jet's engines roar back to life as the maximum forward thrust is reached a few seconds after being commanded. Airspeed starts to increase again, but the aircraft is now only 300 ft from the runway end and below flying airspeed.

In desperation, the captain pulls back hard on the yoke and the airplane is forced in the air, exhausting all the lift reserve the wing could collect. Immediately after liftoff the stick shaker activates.

The aircraft barely climbs to 50 ft agl and is now stalled with a pitch angle exceeding 20 degrees. It crashes about 1500 ft from the runway end after being barely airborne for 6-7 seconds. No one on board survives the accident.

Real versus hypothetical

The above was an imaginary event, but this one really happened. On the morning of Jul 31, 2008, about an hour after powerful morning summer storms had passed through southern Minnesota, a corporate Hawker 800A crashed during an attempted landing at OWA (Owatonna MN). OWA's 5500 x 100-ft concrete Runway 30 has an average downslope of 0.7%.

At the time of the accident winds were reported as light, but just an hour before gusts were being recorded up to 65 kts. Heavy rain was reported too. Two pilots and 6 passengers lost their lives in the crash. NTSB is still investigating, but a likely accident scenario is crystallizing from eyewitness accounts.

It appears that the pilot touched down long and fast. Realizing that he couldn't stop on a wet runway, he attempted to go around. The aircraft apparently never left ground effect and stalled in, crashing about 2500 ft from the northwest end of the runway.

Judging from aerial photos of the crash location, it appears that the Hawker lifted off briefly and then touched down in a cornfield 1500 ft and slightly to the right of the departure end of Rwy 30.

This hypothesis is supported by the fact that there were no visible marks or debris in the field for the first 1500 ft or so. Had the Hawker exited the runway rolling, it would have stopped in a much shorter distance than 2500 ft, since cornfields provide high deceleration.

One problem with runway contamination at small airports is that the pilot doesn't know what to expect until touchdown occurs and while attempting to slow down. And by then it might already be too late.

The point-of-no-return for a successful go-around has been passed, and the aircraft cannot stop nor safely take off on the runway remaining-a sort of ground-equivalent "coffin corner." The fact that the jet in the OWA accident may have touched down long and with excessive airspeed could not have helped.

It may be that the captain realized the aircraft could not stop on the remaining runway. But was attempting a go-around a prudent thing to do? Is there such a thing as an unsafe or impossible go-around?

A question of judgment

Accident statistics show that executing a go-around after touchdown can be fatal. For example, 37 out of the 88 on board were killed in the attempted go-around of an American Airlines Boeing 727 after a long touchdown at STT (St Thomas, US Virgin Islands) in Apr 1976.

Distance covered during constant acceleration or deceleration shown as a function of groundspeed. Low acceleration or deceleration consumes disproportionately more runway than higher values.

The airliner touched down about 3000 ft from the threshold of the 4650-ft runway. After abandoning the braking effort, the captain attempted to go around. Then, realizing that it would be impossible to lift off, the captain changed his mind again and tried to stop.

The 727 exited the runway at high speed, with many fatalities occurring in the ensuing crash and fire. Unfortunately, neither aircraft manufacturers nor airlines provide any guidance or training on if and when to go around after touchdown.

To the best of our knowledge, no standard operating procedures or flight training procedures address this important safety issue. Corporate aviation is especially vulnerable to such events. Business aircraft land on all kind of runways, many of which have no porous friction course (PFC), meaning that even a moderate rain can cause standing patches of water and induce hydroplaning.

In addition, some corporate operators have no built-in landing safety factor as required by FARs for commercial operators-which are not "bulletproof" either. The fundamental question is when and where on the runway is the point-of-no-return for a go-around reached. The aircraft may or may not be able to stop on the remaining runway.

However, if it is slowed below the minimum safe go-around speed, there will not be enough runway remaining for it to become safely airborne either. Therefore, the crew should accept a runway overrun as a lesser evil.

The point-of-no-return and minimum safe speed to initiate a go-around are functions of the runway landing distance available (LDA), actual touchdown point, density altitude, wind, pilot reaction time (ie, decision time), inertia and duration of the configuration change.

A full analytical analysis of this problem is complicated and requires more space. However, we have derived an approximate analytical model and employed few assumptions to predict the minimum go-around speed with reasonable accuracy.

Assuming proper tire inflation, a Hawker 800's hydroplaning speed is just below 100 kts. This means that for groundspeeds in excess of 100 kts the rolling friction deceleration will be on the order of 1 kt per sec (1 kt/s) or about 0.05 g.

Thrust reversers typically provide up to 40% of the average forward thrust. Thus, the maximum possible deceleration while hydroplaning is about 0.20 g (6.45 ft/s2 or roughly 4 kts/s). Average takeoff acceleration, neglecting the rolling friction drag and aerodynamic drag, is 0.33 g (10.60 ft/s2).

We also assumed identical speeds for liftoff (takeoff configuration) and touchdown (landing configuration). The chart at the top of this page shows the rolling distance versus groundspeed for constant acceleration or deceleration.

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