Hello everyone, this is my first ever PPRuNe post!
I’m looking for some insight into the accuracy of
PEP-generated RTOW charts. Has anyone ever come across values that they considered questionable or potentially problematic? A colleague of mine is skeptical of these charts, claiming they sometimes produce “erroneous” results. One example he mentions is
Istanbul LTFM, RWY 17R, at 132 t, attached.
At first glance the numbers may look counterintuitive, but I find it hard to believe that PEP would generate
unsafe speeds. Less precise than FlySmart or other advanced tools, yes, but not unsafe.
Here’s my reasoning: up to
122 t, the aircraft is
not performance-limited, regardless of wind. My assumption is that PEP therefore calculates a set of speeds using a fixed V1/VR ratio and applies them across all wind components.
At
132 t with 10 kt tailwind, a
4-4 limitation appears. Normally we’d expect V1 to decrease with a tailwind, but at
132 t in zero wind, the aircraft is
not performance-limited, so the baseline V1 is relatively high.
In addition, the chart shows an
allowable exceedance of +1.6 t, meaning the software expects you to calculate using
133.6 t, and therefore bumps the V-speeds slightly to reflect that.
This leads to two questions:
- What exactly is the difference between a “4-4” limitation code and a single “4”?
- Why do the V-speeds at 135 t decrease with increasing headwind, instead of the usual trend?
Thanks in advance for any insight!
LGR
