# What do the yellow lashes/wings on the B737 PFD indicate?

When I was looking at a YouTube clip of a B737 doing a landing, I couldn't help but notice something on the PFD:

What do these yellow lashes/wings indicate on the artificial horizon?

Image Source (Added green arrows for question clarity)

They were on for the entire approach and remained on even after touchdown.

## 1 Answer

They display the maximum pitch that can be exercised with the current configuration of the aircraft.

Using data which is measured in modern airliners, a maximum pitch angle can be calculated and displayed to the pilot on the primary display. It is described fully on this page (h/t @mins)

With airplane aerodynamic specific data and the angle of attack measurement, we can have an effective pitch limit indicator PLI. A pitch limit indicator informs the user about the current difference between $max(\alpha)$ and the current $\alpha$. In many commercial airplane the pitch limit indicator is integrated within the glass cockpit, as shown in Figure 3; with this setup the pilot has a real-time indication of how much can pull on the column.

• Does this indicate the limit of pitch, or actually the limit of AoA? – Steve Jul 11 '17 at 17:15
• What are those markings to be compared to? In the video they seem to be "fixed to the screen" while the blue/brown horizon indicater moves behind them? I do not suppose the idea is to tell the pilot "don't pitch more than 12 degrees below the horizon", but then what is it that should be kept from crossing the yellow marks? – Henning Makholm Jul 11 '17 at 17:16
• @Steve If I had to guess, it's the pitch that will result in max alpha. I'm not sure how wing loading is taken into account... I would guess that if you pull up and increase the G loading, then the max pitch angle should decrease even though the max alpha is the same. Increase G loading enough, and you should be able to bring the max pitch angle down to meet the current pitch angle. Again, just guessing. – Wayne Conrad Jul 11 '17 at 17:58