Braking Problem at St Maarten TNCM

[John Pavey 2]

I encounter a braking problem whenever I try landing at Princess Juliana Airport (TNCM).  Essentially, after touchdown, and after retracting thrust reversers, the parking brake is "supposedly" activated and the 777 freeze stops on the runway.  I can't disengage the parking break.  The following are details.

 

Usually I depart from Toronto (CYYZ) with 98,000 lbs fuel and a ZFW load level in the 90% range. On approach, I have configured the aircraft as follows:

 

Spoilers Armed

Autobrake set to 2 (sometimes 3)

Flaps 30

Speed 140

 

On landing, I apply reverse thrust, let the autobrakes do their work, disengage the reverse thrust at 80 knots and tap the breaks around 60 knots.  Around that point, for some strange reason, the parking break is activated! (That is to say, the lower right indicator on the screen says the parking brake is active, even though the actual parking brake is not engaged on the lower pedestal!!).  Once this occurs, the aircraft freezes on the runway.  I have tried the following and am unable to get  the aircraft to move:  1) press period to disengage the parking brake; 2) apply the toe brakes on my Saitek rudder pedals. 3) Click on the parking brake on the lower pedestal to engage the parking brake and then click on it again to disengage the parking brake; 4) try cooling the brakes by clicking on this feature on Screen 2 of the ground maintenance screen on the CDU.  The only action that clears it is to replace the tires (by using this feature in the ground maintenance page of the CDU).  When I do this, the parking brake indicator on the lower left screen disappears and I can then move the aircraft off the runway,

 

It should be noted that this anomaly occurs only when I land at TNCM - at all other locations, my landing procedure is similar (I seldom use autoland) and I don't encounter this problem.

 

Any ideas or suggestions to avoid this annoyance would be appreciated.

 

[77west 139]

Are you using default TNCM or add-on?

[John Pavey 2]

It's the default FSX airport.

[marc0 0]

Strange one that, does it show that your wheel chocks are engaged on the ground connections page?

[John Pavey 2]

I'll check that out when I fly the route tomorrow.  Thanks

[DMullert 216]

Are you disengaging the Autobrake once you come down to about 50-60kts?  I always do because sometimes the Autobrake slows the plane down too fast.  if the runway is long enough I do not use A/B unless runway conditions merit it.

 

Dennis

[troyboy66 66]

I believe this happens when the brakes overheat. I could be wrong but this happened with me once when I manually braked for too longer at higher speeds. The brakes overheated and the parking brakes was automatically applied. This was a one time thing but I quickly resolved it by going into the FMC maintenance window and changing the tires. At that point I was able to taxi the aircraft

 

Troy

[Olympic260 415]

Sounds like your tires have been deflated, due to excessive brake heat.

[John Pavey 2]

Ok - some progress - this time I set the Autobrakes to 1; on touchdown once the autobrakes kicked in, I applied reverse thrust and at about 90 kts, disengaged the autobrakes, disengaged reverse thrust around 80 knots and let the 777 slow before applying the brakes gently till we slowed so I could do a 180 at the end of the runway,  Just prior to the turn, I did get a BRAKE TEMP warning. Coming out of the turn, brakes were off but I noticed the temp was still increasing (albeit very slowly) so at that point, I used the cool brake option under the CDU's Maintenance page 2 and that addressed the problem

 

Don't know why this issue occurs at St Maarten and not the other locations I've landed the 777 (could it be that the runway at St Maarten is overheated due to the sunny climate? (don't think that PDMG would have that degree of realism but hey who knows!!).  At any rate, I will try replicating my typical approach procedure at another airport with a similar size runway (about 7200 ft) and see if this problem reoccurs.  Thanks to your insight - it really helped

If anyone has actually flown a 777 into St Maarten I would love to hear if they need to employ similar braking technique to avoid the brake temp and pressure problem

 

Cheers

[DMullert 216]

Hey John!

 

On an airport like TNCM you may want to hang on to reverse a little longer than 80kts.  Autobrake 1 is fine but let the reverse do it's job through probably 40kts.  I usually turn OFF the AB system once I am down to about 25-30kts. That should save your brakes from overheating.  Are your airbrakes deploying upon touchdown?  TNCM requires full flaps, airbrakes fully deployed, reverse thrust down to 30kts and Autobrake 1 to get the 777 slowed down safely.

 

Dennis

[BrianW 124]

Autobrake 2 is the same at TNCM as anyplace else and shouldn’t overheat. Do you use rudder pedals or the keyboard for braking? Are you manually braking more, earlier or harder than normal? Have you checked the gear synoptic page before landing to confirm you’re starting with temps at or around 0? I’ve been into TNCM (FlyTampa version) several times and have never had an issue. It may seem counter intuitive but have you tried using autobrake 3 and letting it take you to a complete stop?

As a side note the wheels have fuse plugs that melt to let the air out of the tires when they reach 182C to prevent them from exploding. This can happen any time your brake temperature indication is >5.0 (538C).

Brian

[3-2-1-Now 126]

I go to idle reverse at 80 kts and stow the reversers passing 60 kts. You don't want to use them much below that speed otherwise you risk FOD.

 

If your brakes are overheating on Autobrake 2, something is not right as usage with reverse thrust should not generate sufficient heat (in fact the heat registered on the brake temp monitor is delayed by ~10 mins, so you shouldn't use it for peak temperature until after that time). The brake should be "cold soaked" like the rest of the aircraft upon landing, so even if it is hot on the ground, it should not cook the brakes.

 

Best regards,

Robin.

[777simmer 117]

The above info is all correct.

 

Younwant to reach Reverse Idle by the time you have slowed down to taxi speed to prevent FOD damage!

 

If Autobrakes 2 is overheating your brakes, something is wrong!

Unless you are landing downhill and autobrakes two, which is a certain deceleration rate, is having to apply maximum brake pressure to decelerate at that target rate!

[John Pavey 2]

As an update, I've applied most of the really helpful comments above, but so far, my results are as follows:

 

Approach configuration

• Speedbrakes armed
• Flaps 30
• Autobrakes 2
• Autothrottle On - speed set to 138 kts

 

On touchdown:

• confirmed that speedbrakes are deployed
• Reverse thrust engaged
• I deliberately keep my feet off the rudder pedals and let the autobrake do its work
• T7 slows to about 90 kts at which point I note the tires begin to heat up
• At 79 kts, tire temperature readings for the left main gear are above 5.0 while the right main gear are in the 2.0 ranges  (Note that I still have not applied any manual breaking)
• At that point I have no choice but use the CDU Maintenance cool tire option otherwise tires will overheat and the tires explode

I also tried a landing without the autobrake set, applying manual braking on the pedal and got similar results.

 

Again, I don't know why this occurs at TNCM as I usually have no problems landing at other airports.

 

(Incidentally, I tried another trip to TNCM, this time taking off from MDPP in Puerta Plata.  It's interesting, (probably not coincidental) that on the take off roll, tire heat averages began to rise significantly to the point that just prior to lift off, I did get both a BRAKE TEMP and TIRE PRESS warning displayed and notice that the temperature averages for both the left and right main tires was rising above 5.0.  Fortunately, the plane was rotating at that point and I cooled the brakes at that point.  My take off procedure was no different than usual - Toes on the brakes, thrust levers smoothly advance to 55% N1 at which point I engage TOGA and commence the roll.  On all other take offs, I have never had a problem with overheating tires.)

 

So I don't know whether there's a bug in my computer or what, but I will try further tests using both TNCM and other airports to see if I can understand what it causing this.   In the meantime, thanks for all your helpful comments  -so even provided me with information I never knew existed about the T7 brakes.

[Mike777 163]

Hi, John,

 

I am wondering whether the problem might be starting on takeoff when you hold the brakes (if I understand you correctly) while bringing thrust up to 55%.  If you are already  getting a low tire pressure warning on takeoff, maybe your tires are already partially deflated on landing.  Flying would cool the brakes, but I don't see how it would refill the tires.

 

My brake and tire problems occur after departing the runway, due to excessive braking, braking with thrust more than idle, and I think failing to completely shut down the autobrake. 

 

Robin or Rob, what is "FOD" please?

 

Mike