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Home » Portals » Operational Issues » Runway Excursion
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The flight crew’s inability to assess or to manage the
aircraft’s energy condition during approach is often cited
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as a cause of unstabilised approaches. Crews should
appreciate that fatigue will increase the likelihood that they
will have difficulty in detecting that an approach is going
outside normal parameters.
Either a deficit of energy (low and/or slow) or an excess of
energy (high/fast) may result in an approach-and-landing
incident or accident involving one of the following:
Loss of control;
Landing before reaching the runway (Undershoot on
landing);
Hard landing;
Tail strike; or,
Runway overrun.
These safety occurrences can result from one or more of the
following factors:
Excessive sink rate
Incorrect flare technique (late or early flare initiation etc.)
Excessive airspeed
Incorrect power management (inappropriate thrust on
final approach (too high/too low) power-on touchdown)
Loss of visual references
Runway
Excursion
Content
control:
The
Air
Pilots
FEEDBACK
Energy Management During
Approach
Statistical Data
The Flight Safety Foundation (FSF) Approach-and-landing
Accident Reduction (ALAR) Task Force found that
unstabilised approaches (i.e. low/slow or high/fast
approaches) were a causal factor in 66% of 76 approachand-landing accidents and serious incidents worldwide in
1984 through 1997.
These accidents involved incorrect management of aircraft
energy, resulting in an excess or deficit of energy, as follows:
Aircraft were low/slow on approach in 36 percent of the
accidents/incidents; and,
Aircraft were high/fast on approach in 30 percent of the
accidents/incidents.
Aircraft Energy Condition
Aircraft energy condition is a function of the following
Airspeed and airspeed trend;
Altitude (or vertical speed or flight path angle);
Drag (caused by speed brakes, slats/flaps and landing
gear); and,
Thrust.
One of the primary tasks of the flight crew is to control and
to monitor aircraft energy condition (using all available
references) to:
Maintain the appropriate energy condition for the flight
phase (i.e., configuration, flight path, airspeed and thrust);
or,
Recover the aircraft from a low-energy condition or a
high-energy condition.
Controlling aircraft energy involves balancing airspeed,
thrust (and drag) and flight path.
Autopilot modes, flight director modes, auto throttle
modes, aircraft instruments, warnings and protections are
designed to relieve or assist in this task so it is essential that
flight crews have a thorough understanding of these modes,
their potential and limitations.
FEEDBACK
primary flight parameters:
Going Down and Slowing Down
It is important to understand your aircraft. Some modern
airliners are so aerodynamically ‘clean’ (low drag) that it
may not be so much a case of ‘going down and slowing
down’ as ‘going down or slowing down.’
A study by the U.S. National Transportation Safety
Board revealed that maintaining a high airspeed to the
outer marker (OM) may prevent capture of the glideslope
by the autopilot and may prevent aircraft stabilisation at the
defined stabilisation height.
Nonetheless, ATC instructions to maintain a high airspeed to
the OM (160 knots to 200 knots, typically) are common at
high-density airports, to increase the landing rate. The study
concluded that no airspeed restriction should be imposed
by air traffic control (ATC) when within 3 to 4 nm of the OM,
especially in instrument meteorological conditions (IMC).
Energy management is the responsibility of the pilot in
aircraft’s inertia, limitations and crew ability in the
prevailing environmental conditions. Wind can play an
important part. There can be a big difference in outcome
between maintaining 160 knots to the marker with a 30
knots headwind and with a 20 knots tailwind. When ATC
instructions are at variance with the PIC’s responsibilities
and cannot be complied with, this must be communicated
to ATC immediately.
Aircraft Deceleration Characteristics
Although deceleration characteristics vary among aircraft
types and their gross weights, the following typical values
can be used:
Deceleration in level flight:
With approach flaps extended: 10 knots to 15 knots per
nm; or,
During extension of the landing gear and landing flaps:
20 knots to 30 knots per nm and,
Deceleration on a three-degree glide path (for a typical
140-knot final approach groundspeed, a rule of thumb is
FEEDBACK
command (PIC) who must take into consideration the
to maintain a descent gradient of 300 feet per nm/700
feet per minute [fpm])[1]:
With approach flaps and landing gear down, during
extension of landing flaps: 10 knots to 20 knots per nm;
Decelerating on a three-degree glide path in a clean
configuration is not possible usually; and,
When capturing the glideslope with slats extended and
no flaps, typically a 1,000-foot descent and three nm
are flown while establishing the landing configuration
and stabilizing the final approach speed.
In some aircraft, speed brakes may allow a faster
deceleration (but often the use of speed brakes is not
recommended or not permitted below 1,000 feet above
airport elevation or with landing flaps extended). However,
the deceleration effect of all drag devices (spoilers, flaps
and landing gear) becomes less effective as speed reduces.
Typically, slats should be extended not later than three nm
be configured for the approach being flown in accordance
with the aircraft’s Flight Manual/Flight Training
Manual/Operations Manual.
The diagram below shows aircraft deceleration capability
and the maximum airspeed at the OM based on a
conservative deceleration rate of 10 knots per nm on a
three-degree glide path.
FEEDBACK
from the final approach fix (FAF). In all cases, aircraft should
Typical schedule for deceleration on three-degree glide
Foundation
For example, in IMC (minimum stabilisation height, 1,000
feet above airport elevation) and with a typical 130-knot
final approach speed, the maximum deceleration achievable
between the OM (six nm) and the stabilisation point (1,000
feet above airport elevation and three nm) is:
10 knots per nm x (6 nm – 3 nm) = 30 knots.
To be stabilized at 130 knots at 1,000 feet above airport
elevation, the maximum airspeed that can be accepted and
can be maintained down to the OM is, therefore:
130 knots + 30 knots = 160 knots.
Whenever a flight crew is requested to maintain a high
airspeed down to the outer marker (OM), a quick
computation such as the one shown above can help assess
the ATC request.
Again, an understanding of the prevailing wind is important;
a crosswind on the runway may be a substantial tailwind
above a thousand feet.
Back Side of the Power Curve
FEEDBACK
path from outer marker to stabilisation height - Flight Safety
During an unstabilized approach, airspeed or the thrust
setting often deviates from recommended criteria as
follows:
Airspeed decreases below VREF; and/or,
Thrust is reduced to idle and is maintained at idle.
Thrust-required-to-fly Curve
The diagram below shows the thrust-required-to-fly curve
FEEDBACK
(also called the power curve).
Thrust Required to fly a 3 degree glide path in landing
configuration
The power curve comprises the following elements:
A point of minimum thrust required to fly;
A segment of the curve located right of this point; and,
A segment of the curve located left of this point, called
the back side of the power curve (i.e., where induced drag
requires more power to fly at a slower steady-state
airspeed than the power required to maintain a faster
airspeed on the front side of the power curve).
The difference between the available thrust and the thrust
required to fly represents the climb or acceleration
capability.
The right segment of the power curve is the normal zone of
operation; the thrust balance (i.e., the balance between
thrust required to fly and available thrust) is stable.
Thus, at a given thrust level, any tendency to accelerate
increases the thrust required to fly and, hence, returns the
aircraft to the initial airspeed.
Conversely, the back side of the power curve is unstable: At
a given thrust level, any tendency to decelerate increases
the thrust required to fly and, hence, increases the tendency
to decelerate.
The final approach speed usually is slightly on the back side
of the power curve, while the minimum thrust speed is 1.35
times VSO (stall speed in landing configuration) to 1.4 times
VSO.
It is important that if a high/low energy state approach
prompts a decision to go-around, the flight crew must
commit to completing the go-around and not subsequently
change the decision in an attempt to land. (A change of
decision is often observed when the decision to go-around
is initiated by the first officer (as PF) but is overridden by the
captain.)
Runway overruns, runway overshoots, collisions with terrain
and obstructions often are the consequences of decision to
land after a go-around is initiated.
The only Go Around you will ever really regret is the one
that you did not do when you should have done.
SKYclip
FEEDBACK
The Go-Around Decision
Speedcontrol for
final approach
Related Articles
Hard Landing
High Energy Approach Monitoring System
Landing Flare
Flight Safety Foundation ALAR Toolkit
Global Action Plan for the Prevention of Runway
Excursions (GAPPRE), 2021
Further Reading
DGAC (France)
Approaches - DGAC has published three documents in
the English language related to non-stabilised
approaches.
Flight Safety Foundation
ALAR Briefing Note 7.1 - Stabilized Approach
ALAR Briefing Note 8.1 - Runway Excursions and Overruns
Reducing the Risk of Runway Excursions - Report of the
Runway Safety Initiative
Runway Excursion Risk Awareness Tool
Non-stabilized Approach After ATC-Requested Runway
Change (OGHFA SE)
Runway Overrun On Landing (OGHFA SE)
Landing with tailwinds can produce some interesting and
counter-intuitive shear effects, which give very good
reason to monitor, and possibly over-ride, the actions of
the auto-throttle if it is engaged. See: "Tailwind Traps",
Aerosafety World article, March 2007.
Airbus Safety Library
FEEDBACK
DGAC (France) Publications on Non-Stabilised
Airbus Approach Techniques Briefing Note - Flying
Stabilized Approaches
Control your Speed… During Descent, Approach and
Landing, Airbus Safety First Magazine, #24, July 2017
HindSight Articles
HindSight4 - Economy versus Safety - the Professional’s
Dilemma
CANSO Information Flyers
Runway Excursions - An ATC Perspective on Unstable
Approaches
Avoiding Unstable Approaches - Important Tips for ATCOs
Flight Data Services Case Study
Case Study 6: Winglets and Low Power Approaches
EASA
Awareness and Energy State Management"
GAJSC
Approach and Landing by General Aviation Joint Steering
Committee (GAJSC) Loss of Control Work Group
Boeing
The first half of "Reducing Runway Landing Overruns",
Boeing Aero magazine Q3/2012 is well worth reading.
NASA
Aircraft Loss of Control: Causal Factors and Mitigation
Challenges, by S. R. Jacobson, NASA, 2010
Notes
1. ^ Approximate descent rate required can be calculated
from Groundspeed ÷ 2 x 10. E.g. 140kts = 700fpm and
100kts = 500fpm .
FEEDBACK
EASA SIB 2010-33: "Flight Deck Automation Policy - Mode
Categories:
Runway Excursion, Veer Off, Overrun on Landing, Loss of
Control, Controlled Flight Into Terrain
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