AAL 1632 Overrun at KDFW, 2/10/2024
 

Given the recent UAL maintenance scrutiny, this incident involving a AAL 737NG “brake system anomaly” is worth noting. Post incident, hydraulic and electrical problems were discovered on the brake system, likely the result of a maintenance action on 2/6/2024.

Aircraft ended up in the overrun area of 17L at DFW. Might have been more interesting if this had occurred (landing or RTO) at the flight’s departure airport, DCA (7100 ft), instead of DFW (8500 ft).

NTSB Aviation Investigation Preliminary Report - AAL 1632, N991AN

Data also showed the engine 1 and 2 thrust reverser parameters [Eng1
and Eng2 TR Dply-DEU] transitioned from “stowed” to “deployed” about 8 seconds after
touchdown. They remained deployed for about 12 seconds, were stowed for about 6 seconds,
and then re-deployed for the remainder of the landing rollout.

Does someone have an, ahem, "educated guess" on AAL's 737 thrust reverser use language? Specifically, when to stow.

Good job it wasn’t landing at Midway!

Most US airlines want reverse reduced to idle at 80 knots. Mostly for FOD prevention. Many pilots choose to come completely out of reverse at that point. I suspect based on reverse on this flight they came out at 80 knots, realized they were not getting proper wheel braking and reinstated reverse at that point.

But is it official SOP or just normalized deviation? Could you post manual language with that verbiage?

How many legs were flown after the maint. work and why didn't the faults show up right away ?...

Looks to be about 15 flights after aircraft positioned from TUL to DFW.

I seemed to remember new checks were introduced long time back which might have involved spinning up wheel transducers (the original Maxaret worked on the wheel it was fitted to, so no cross over issue).
Similar incident "Runway overrun following brake failure, Boeing 737-247, January 19, 1995 at ATL" same airline and more basic model.
Also On Oct. 17, 2019, PenAir flight 3296, a Saab SA-2000, Alaska.
Found this instruction post A320 minor miss-hap when more than one transducer is changed.
NOTE : If the MLG WHEEL TACHOMETER DRIVING TOOL is not available, as an alternative you can use:
- two standard drilling machines with the DRIVING ADAPTOR (98D32403004000).

From the B 717 FCOM: For a normal landing at 80 KIAS smoothly move reverse levels to be in reverse idle detent by 60 KIAS.
At 60 KIAS move reverser levers to forward idle thrust position and stow by 40 KIAS.

My airline (US large Cargo Airline) has changed our thrust reverser normal procedure to just going to reverse idle until 60 knots under “Normal” conditions. We can use full reverse thrust at our discretion whenever we feel the need, but on a normal landing, just reverse idle is sufficient. From what we were told, this procedure is becoming an industry standard as it reduces engine wear. Perhaps this could explain the strange reverser deployment in this incident.

The N1 plot is kinda hard to read with accuracy, but it looks like the N1 was at 82%, or maximum reverse when the TRs were deployed.

I no longer have access to the various FCOMs, but I believe that is common to all Boeing models.

The important thing is to get the reversers out as soon as practical after touchdown - even at reverse idle the ram drag at landing speeds is huge.
Because of that velocity squared thing, the ram drag (and hence the reverser effectiveness) drops rapidly as you slow - plus if you have any reverse thrust asymmetry, directional control can become difficult as you slow and you lose rudder effectiveness.

Thanks BFS...The prelim report mentions wiring as well as mechanical issues after the maint... Still curious if any issues popped up during the previous legs?

Interestingly, the deceleration on the DFDR plots is constant from the TR deploy until they’re stowed the first time. I would have thought it would be steeper at high speeds given the brakes weren’t working and the TRs were at Max.

Remember that velocity squared thing applies to kinetic energy as well - there is four times the kinetic energy at 120 knots that needs to be dissipated as there is at 60 knots...

Excellent point. Thanks.

In normal use since auto brakes maintain a deceleration rate there is often little or no wheel brake action at higher speeds. If full reverse is used that will meet the deceleration rate called for at lower auto brake settings. As the aircraft slows and reverse thrust becomes less effective or is phased out wheel braking increases to maintain the same deceleration. What is a bit odd in this incident is they appear to have wheel brakes functioning as they went off the end. I have long forgotten my 737 systems so perhaps they were able to manually select a alternative mode.

I've flown different Boeings with different airlines, and the FCOM has always stated: "By 60 knots, start movement of the reverse thrust levers to be at the reverse idle detent before taxi speed".

Airbus (at least on the 320 series) says 70 knots to select idle.