Cockpit Window Heat - Bird Strike Risk

[An Paddy Eile]

I know this has been discussed to some extent before, but can you tell me what your aircraft says in the MEL, QRH or other source regarding restrictions when the window heat is inoperative prior to departure or when it fails inflight?

On the A320, the failure requires nothing more than an ECAM caution for crew awareness and no speed restrictions apply. Yet, many (if not most) believe that speed should be limited to prevent failure of the window if a birdstrike should occur. Why then, do Airbus not say so?? I'd be interested to see what other manufacturers say....

Thanks!

APE

[Denti]

737 classic has a restriction of 250kias below 10.000 if window heat is off, u/s or in an overheat state.

[idg]

When I asked Airbus exactly this question their reply was that the windscreens had been tested at 350+ knots and cold.....therefore no problem!

Also told that this was 'industry practice' now...can anyone shed light on this statement?

:ok:

[spannersatcx]

330/340 42-03 Front Windshield Heating One may be inoperative provided: The aircraft is not operated in icing conditions.

B747 30-11 Flight Deck Window Heating
1) #1 Windows One may be inoperative provided:
a) #1 left window heat is operative for LWMO,
b) Flight is not dispatched into known or forecast icing conditions,
c) Windshield air (anti fogging) is operative, and
d) Both #2 window heaters operate normally.

B747-400 30-41-2 FLIGHT DECK WINDOW HEATER SYSTEMS (#1 & #2)
One #1 or one #2 window heater may be inoperative provided:
a) Operation is not predicated on flight into known or forecast icing,
b) Windshield air (anti-fog systems) operates normally, and
c) Remaining #1 AND #2 window heaters operate normally

B777 [30-41-1 Flight Deck Forward Window Primary Heater Systems
One may be inoperative provided:
a) Associated window backup heater operates normally,
b) Both left and right side (#2) window heaters operate normally,
c) Aircraft is not operated in known or forecast icing conditions, and
d) For a cracked outer glass ply, limit airspeed to 280 KIAS or less below 10,000 FT MSL

[An Paddy Eile]

Idg,

That's what I had heard also, although I heard it at least third hand!!

I wonder was it something that only applied to the old classics then??

Does anyone have any references???

[lomapaseo]

Be careful of applying light switch (on-Off) reasoning to certification standards applied to enviromental conditions (birds, ice, etc.)

The idea behind the standard is to make it [i]likely['] that you will survive an encounter, not necessarily to guarantee it for all encounters. Thus there can be a stack up of conditions for or against you surviving (bird mass, velocity, condition of windscreen, etc.) If any of these conditions are crtical variations and can be reasonably controlled then the SOP (avoidance) will be stipulated by the manufacturer. The significance (criticality) of two or more conditions is the conditional probability of encountering them at the same time. If this were to significantly increase risk, then it would typically be considered in the MEL

[Avi8tor]

Modern windscreens largely not affected strenghtwise regardless of heating on or off.

Used to be a fav airline interview question.

[QAR ASR]

The biggest risk with window heat off is Frostbite. I've spent a few long sectors on the 320 with it u/s and its like sitting in front of an open freezer for a day, I had to wear my jacket and hat (Hats, oh those were the days);)

[vapilot2004]

While I am unsure of the relationship to speed limitations with U/S windshield heat, the Sierracin system on the 737 has two independent heating 'elements' per window while the A320 uses only one.

The DC-9 and MD-80 also carried a speed limitation of 315kts :eek: below 10,000.

[An Paddy Eile]

lomapaseo,

I agree with your post. Meeting the south end of northbound swan while at 350 KIAS will probably mean big trouble regardless of whether your window heat is working or not. But, as there is no speed restriction stated in ECAM or the MEL then it must be safe to assume that the risk has not increased significantly.

If the certification requirements involve a bird carcass of a particular size and the window meets the requirements with heat ON then it would surely be a simple process to include a speed restriction for a heating failure which is statistically unlikely to happen all that often. The fact that no restriction exists speaks volumes.

So why is it that so many pilots feel it necessary (as I found out recently) to reduce speed to minimum clean or lower, refuse ATC speed control above this and try to stay as high as possile for as long as possible during the approach, even though no restriction is stated anywhere?? They must have got the idea from somewhere?? Was there a restriction on their previous aircraft?? Was this a problem that used to exist but has been solved now by modern manufacturing methods?????

[omnidirectional737]

767 limitation for bird strike protection 313knots below 8000ft with window heat on or off.

[lomapaseo]

So why is it that so many pilots feel it necessary (as I found out recently) to reduce speed to minimum clean or lower, refuse ATC speed control above this and try to stay as high as possile for as long as possible during the approach, even though no restriction is stated anywhere?? They must have got the idea from somewhere?? Was there a restriction on their previous aircraft?? Was this a problem that used to exist but has been solved now by modern manufacturing methods?????

The issue with higher speed at low altitudes places the intuitive risk way out of kilter with the historical experience regarding the airframe. It's not an engine issue since higher aircraft speeds, above 200 kts, often will reduce the fan blade damage. the larger issue is the likelihood of causing significant structural damage and taking out multiple critical hydraulic systems with multiple birds. heretofor the aircraft design, meeting the existing spec, accomodated this risk statisticaly. However everything has its limit and now days with the increased robustness of the new engines, the most likely acrchiles heel in a multiple bird strike above V1 is the aircraft itself. Increasing the aircraft speed above 250 kts at low altitude flock encounters greatly increases this risk statisticaly.

[An Paddy Eile]

If the worry was airframe related and the risk was statistically large enough, then surely every manufacturer would have placed a speed limit below 10,000ft or some other reasonable altitude. There is no doubt that bird strikes are a risk, but increasing speed only increases the risk of significant damage following an encounter. It does not significantly increase the likelihood of the encounter itself. So, the significant, damaging, bird strike risk must be acceptably low if maufacturers have not applied general speed limits.

I for one, given the opportunity, will always increase speed to the best econ climb speed as soon as I am able. Many do not agree with this practice.

But, my previous question, related specifically to those who are happy to fly at high speed below 10,000ft with everything working, but suddenly want to slow down when the window heat fails, even though the aircraft manufacturer does not state any extra limitations whatsoever.

So, do these people have a point? Or are they falling back onto outdated theory and practice from previous machinery? Can my Airbus creep up on an unsuspecting bird from behind at 340 Knots and give it a slap with it's cold, unheated windshield and have nothing more than mess to deal with?