737NG Speed restrictions
 

Can anyone enlighten me about a conversation I had with a neighbouring ATCC yesterday?

It concerned a 737-900 which was crusing at FL 240 and was speed-restricted to 270 KIAS. The controller said that this is the case with all the 737NGs and had something to do with icing. It was news to me, and if it is a blanket restriction it can cause problems when I try to get one to do 300kts+ to keep him in his place in a stream.

Can someone confirm or deny this and give a little more detail?

Thanks.

Airworthiness Directive 2002-08-20

The FAA has received reports of numerous incidents of
severe airframe vibration, or limit cycle oscillation (LCO), in flight after the horizontal stabilizer had
been deiced/anti-iced on the ground. The reported incidents occurred on Boeing Model 737-600, -
700, and -800 series airplanes. The empennage structure on these, as well as Model 737-700C series
airplanes, is identical; therefore, all of these airplanes are subject to the identified unsafe condition.
These events have been attributed to an accumulation of deicing/anti-icing fluid or other residue in
the elevator balance panel cavities and on the external surfaces of the elevator tab. The accumulation
of fluid in the balance bays has been attributed to inadequate drainage provisions. Drainage
provisions on Model 737-900 series airplanes are improved over those on the airplanes affected by
this AD.
Preliminary results of the investigation of the incidents indicated that only Type I and Type II
deicing/anti-icing fluids were susceptible to this type of accumulation; however, a recent LCO event
occurred following deicing/anti-icing with Type I and Type IV fluid on one affected airplane. One
operator reported finding up to 30 liters of fluid trapped in the balance bays on one airplane. Other
operators have reported visible accumulations of foreign substances on the external surfaces of the
elevator tab. The additional weight of accumulated residue on the tab can initiate LCO. The elevator
tab is so aerodynamically sensitive that repairing and painting the subject area have been prohibited
by related existing ADs. The reported airspeeds at the onset of the incidents have ranged from 276 to
325 knots.
Fluid or residue accumulated in the balance bays, or foreign substances accumulated on the
external surfaces of the elevator tab, in combination with normally recommended maximum
operating airspeeds, can initiate LCO or flutter and result in loss of controllability of the airplane.



"After any ground deicing/anti-icing of the horizontal stabilizer, airspeed must be limited to 270 KIAS until the crew has been informed that applicable maintenance procedures have been accomplished that would allow exceedance of 270 KIAS. Once the applicable maintenance procedures have been accomplished, exceeding 270 KIAS is permissible only until the next deicing/anti-icing."

Briefly...
 

I believe that the following is true for UN-MODIFIED NG aircraft:

(i) speedbrake limited to 300kts IAS
(ii) Following ground de-icing, speed limit 270kts IAS until inspection of empennage carried out (approx one hour job using cherry-picker).

Just for comparison (calls for 'QRH, non-normals, facial muscular, tongue must be placed firmly in cheek, recall actions...'), here is a comprehensive guide to outstanding emergency speed restrictions applying to Airbus aircraft:

(i)
(ii)
(iii)
(iv)
(v)
(vi) etc

Hope that helps!

Thanks for the replies so far. Interesting, except that overnight temperatures in this part of Europe have not fallen below +9 deg C for weeks and the ground temperature at the time was approximately +14 deg C!!

Could it just have been a misunderstanding by the crew/ATC?

Hy,

The speed restriction apply as long as you perform the maintenance procedure even when you fly a week after de/anti-icing. Maybe the A/C was de-iced at a remote station. To get rid of the speed restriction takes youonly a few minutes if equipped with a cherry picker a sponge and a bucket of water but many operators have not implemented a procedure yet....

yours,

Ta very much. Seems a good idea: Design a multi-million dollar aircraft that has to have a maintenance inspection (sic) after every time you spray it with glycol or whatever before it can fly at its design speed.

A few red faces at Boeing, one wonders?:o