Aviation Safety Newsletter - Volume 2, No. 1

Submitted by on Wed, 01.11.2006 - 00:00

Managing Takeoff Risks

by Roger M. Delisle

Those few first seconds after the wheels leave the ground is an exhilarating time for many pilots, but they can also be the riskiest of the flight.  The 2005 Nall Report shows that in 2004, in nearly 1 out of 5 pilot-related fatal accidents (19.4%), the emergency began during takeoff, before the initial climb.  That’s a very short period of time for such a high ratio of mishaps to occur, and it shows how something going wrong like an engine failure when you’re so close to the ground can quickly turn awry.  But there’s a catch word in the statistic I quote above:  Pilot-related.  That is, an accident that arises “from the improper action or inaction of the pilot”1.

In this first of what I hope to be many safety-related articles, I’ll cover how instructors at Rockcliffe are providing a more detailed look at a safer way to plan the takeoff, one which better prepares pilots for quick decisions during those critical first seconds of flight. This is inspired by an incident at our airport earlier this year which, as with most safety-related occurrences, make many pilots think, “What would I have done under these circumstances?” The safest pilot would go further and ask, “How can I learn from this incident, and is there room for improvement in the way I fly so that I can minimise risk under similar circumstances?”   To that end, let's review the incident.

What happened?

At approximately 10:50 EDT on April 21st, a student pilot flying solo in a rental aircraft experienced power drops immediately after lift-off from runway 09 at Rockcliffe.  The pilot, who did not think there was sufficient runway to reject the takeoff, elected to continue the flight with what appeared to be sufficient power to do so. He executed a tight circuit to return to the field and landed without further incident.

Maintenance investigation revealed that the power drop was caused by a worn-out fuel selector valve, whereby the detent wasn't detected by the pilot when selecting both tanks.  This resulted in the pilot inadvertently placing the valve in a partially closed position during pre-takeoff checks.  The offset selector had no effect during the pre-flight engine run-up, most likely because the fuel flow at that throttle setting is lower than at full power during takeoff.  For me, this certainly reinforces the habit which I was taught many years ago, that of slightly rocking the fuel selector valve back and forth a few times to ensure it’s at the center of the detent position.  From this incident, we can also learn that, if the detent is hard to find due to wear, we should be alerted to the risk of partially obstructing fuel flow and either check for this with a high-RPM run-up, or if unsure, return the aircraft for maintenance.  That being said, an incident like this can remind us of the risk of engine problems regardless of the cause, so we'll now concentrate on a generalised technique for a safer takeoff.

Reviewing the Takeoff

The incident helps us imagine a variety of similar “what-if” scenarios and the actions to be taken during takeoff.  For example, what if the engine failure had been complete?  What if it occurred earlier, or later in the takeoff phase?  There are very few, precious seconds to react and to make a decision in case of an unforeseen situation, so carefully planning the takeoff before each flight and a thorough pilot briefing before rolling on the runway will help you react more quickly and correctly should something come up.

Here, we're interested in calculating two particular values that allow the most consistent course of action in:

  • electing to take off in the first place; and
  • continuing or rejecting the takeoff once rolling on the runway.

These values are:  The Accelerate/Stop Distance, and the Go / No-Go Decision Point.

The strategy here is to determine these two values before each flight, then ensuring that we apply them to the available runway.  As we explore this in more detail with a concrete example, it's very important to remember that the rules of thumb given here are based on our instructors' experiences, and corroborate well with other educational sources, but the values they yield have not been officially approved by any aircraft manufacturer.  Our instructors have simplified the calculations here, with the intent of making them easier to get than by using complex performance data charts.  We pilots are then more likely to use them as part of our everyday flying if they're kept simple.

Determining the Accelerate/Stop Distance:

It is the distance needed for a safe takeoff, allowing for a rejection at lift-off.  To calculate it, you take the maximum performance short-field ground run published in your aircraft's Pilot Operating Handbook, add to it the short-field landing distance, again from the same source, then multiply the sum by 1.5 to add a safety margin:

Daccelerate/stop = (Dshort-field ground run + Dshort-field landing) X 1.5

So for example, taking off from Rockcliffe in a Cessna 172M, at maximum gross weight , that aircraft's POH gives interpolated values of 912 ft for the ground run, and 534 ft for the landing distance, both at 20ºC and assuming standard pressure.  Using the formula above, we get:

Daccelerate/stop = (912 + 534) X 1.5 = 2169 ft

which is available from CYRO's 3300-foot runway.  This distance tells us the length needed if we were to abort the takeoff immediately after leaving the runway, and allowing for reaction time and the fact that your flaps are not fully extended.  Keep in mind that the landing distance we used was a maximum performance value, meaning hard braking once you're back on the runway so you don't go past the end.

While planning a trip, you can also use the Accelerate/Stop distance calculation to help you decide where not to land in the first place, and so avoiding tougher takeoff decisions afterwards.

The Go / No-Go Decision Point:

It's the point along the runway at which you make the final decision on whether or not  the takeoff will continue, based on whether or not the aircraft has left the ground.  The value is calculated as a distance from the departure end of the runway, or from wherever you apply full power.  It's simply the takeoff ground run distance from your POH, with an added 50% margin as a simple way of turning that short-field value into a normal takeoff run:

DGo-NoGo = Dshort-field ground run X 1.5

If the short-field ground run distance used above, Dshort-field ground run , is more than half of your available runway, you should use the short-field technique for your takeoff, in other words:

if Dshort-field ground run > ( Drunway / 2 )   then    DGo-NoGo = Dshort-field ground run

So, using our example from above, we test that:

Is 912 ft  >  ( 3300 / 2 )  ?  No.

Therefore we won’t need to perform a short-field takeoff. We then get using the formula:

DGo-NoGo = 912 X 1.5 = 1368 ft

which is the distance along the runway where the wheels should be off the ground.  We then determine a visual reference that matches that distance from the departure end of the runway.  So at Rockcliffe, our Go/No-Go distance is reached about where the museum buildings begin, and this happens to be true for either runway.

Going a bit further into the accelerate-stop distance, let's also determine about where on the runway the aircraft has enough distance to land and stop if you abort the takeoff immediately after lift-off:  Our Dshort-field landing distance is 534 feet, which is about where the first turn-off intersections are from each end of the runway at Rockcliffe.

When using your POH for distance figures, don't forget to consider factors than may increase them, such as aircraft age, pressure and density altitudes, runway surface conditions, etc.

So let's summarise the takeoff decisions we've learned here:

  • Do we have sufficient runway length for our accelerate/stop distance?
  • Is the runway length at least twice as long as our Dshort-field ground run distance?  If not, perform a short-field takeoff.
  • Are we airborne by the time we've reached the museum buildings, our go/no-go decision point? 
    • If no, immediately abort the take off.  A key word here is immediately, as any delay in the decision to abort will quickly eat up what could otherwise be enough runway length to get out of a bad situation.
    • If yes, and if we have a failure after lift-off, is there more than our Dshort-field landingdistance remaining ahead of us, and are we low enough to glide down to use it? 
      • If yes, land, braking hard on your rollout.
      • If no, an off-airport landing straight ahead is likely to be your best bet.

Even if takeoff failures aren't likely, they're possible, so making a habit of being prepared on every takeoff with these easy calculations will put the odds in your favour if you do encounter one, and will make those first few seconds of flight safer.

1 Nall Report, 2004, available from www.aopa.org

Disclaimer:  The sole purpose of this Safety Newsletter article is to educate pilots and other persons involved in civil aircraft operations, strictly in the interest of promoting flight safety.  It is not intended as a substitute for any official investigative report which may or may not exist relating to any incident mentioned. In no way should it be interpreted as apportioning civil or criminal responsibility on any party, including, but not limited to, manufacturers, suppliers, operators, pilots, maintenance personnel or governmental authorities.