That REXFFA is not as 95% of the other ones – crap -, but very interesting, and the guy who filed it was also quite aware of the problem.
A CRESAG (a safety notification to DGAC) as been filed following this one,
Here is the french content and its moogletrad:
Description de l’évènement :
Je réalisais un vol en navigation de LFzz vers LFxx, vol sans problème. Au retour vers LFzz, environ 2 minutes après le décollage pendant la montée, j’ai le voyant d’alerte CED (Control Engine Display) qui s’allume et le CED indique une alarme surchauffe liquide de refroidissement (Led rouge). Immédiatement je réduis la puissance (vers 50%), comme il est écrit dans le manuel de vol, et je passe en palier.
Lorsque je remonte les yeux sur les voyants d’alarme, les deux voyants rouges FADEC clignotent et le voyant rouge alternateur est allumé.
Je décide de faire immédiatement demi tour vers LFxx et réduit complètement la puissance.
Pendant le virage le voyant rouge liquide de refroidissement bas niveau s’allume également.
Je m’annonce en emergency sur la fréquence de LFxx (auto-info) et, étant assuré de ma trajectoire moteur réduit, j’annonce me poser à contre QFU (longueur de piste et vent compatibles) pour éviter d’avoir à utiliser le moteur.
Une fois au sol je dégage la piste et coupe immédiatement le moteur.
Pendant la descente la température du liquide de refroidissement a légèrement réduit de la deuxième vers la première Led rouge.
La visite après vol montre des morceaux de fil tressé et de caoutchouc noir qui sortent sous le capot moteur.
Je préviens notre atelier et, au vu des photos, le chef d’atelier me dit que c’est sans doute la courroie d’entrainement des accessoires (alternateur et pompe à eau) qui a cassé. Il semblerait que ce soit la première fois pour l’ensemble des moteurs Thielert.
Commentaire du déclarant :
Dans le manuel de vol cette panne n’est pas envisagée, il n’y a donc aucune procédure associée.
La rapidité et la « brutalité » avec laquelle les alarmes se sont enchainées peuvent sans aucun doute déstabiliser un pilote avec peu d’expérience.
La procédure « surchauffe liquide de refroidissement » est prévue pour un moteur qui aurait une surchauffe en montée (ce qui est déjà arrivé sur ce type de moteur) et qui permet de faire revenir la température vers la normale.
La procédure « bas niveau de liquide de refroidissement » (fuite envisagée) (ce qui est déjà arrivé sur ce type de moteur) implique un déroutement vers le terrain le plus proche, éventuellement une IVV, mais la température moteur reste stable tant qu’il y a suffisamment de liquide.
Dans le cas de la panne de pompe à eau le moteur passe immédiatement en surchauffe et peut « casser » dans les minutes qui suivent si on ne le met pas au ralenti.
Comme précisé plus haut, le voyant rouge liquide de refroidissement bas niveau s’allume également, Il a fallu rajouter 1,5 litre de liquide pour compenser la perte par ébullition (contenance 5 litres). Le temps de fonctionnement du moteur au ralenti après la panne moins de 3 minutes.
Je pense qu’il faudrait envisager deux possibilités dans la protection contre ce type de panne.
Une formation associée à une procédure d’URGENCE qui permette au pilote de savoir qu’il va devoir effectuer immédiatement un atterrissage d’urgence.
Une modification du circuit de refroidissement par adjonction d’une pompe à eau électrique à mettre en œuvre comme la pompe à carburant en cas de panne moteur (interrupteur) ou en automatique (baisse de pression) avec voyant de déclenchement.
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I carried out a navigation flight from LFzz to LFxx, flight without problems. On the way back to LFzz, about 2 minutes after takeoff during the climb, I have the CED (Control Engine Display) warning light coming on and the CED indicates a coolant overheating alarm (red LED). Immediately I reduce the power (around 50%), as it is written in the flight manual, and I go into level flight.
When I look back up at the warning lights, both red FADEC lights are flashing and the red alternator light is on.
I decide to immediately turn back towards LFxx and reduce the power completely.
During the turn, the red low coolant level warning light also comes on.
I announce myself as an emergency on the LFxx frequency (auto-info) and, being assured of my reduced engine trajectory, I announce that I am landing against QFU (compatible runway length and wind) to avoid having to use the engine.
Once on the ground I clear the runway and immediately cut the engine.
During the descent the coolant temperature slightly reduced from the second to the first red LED.
The post-flight inspection shows pieces of braided wire and black rubber sticking out from under the engine hood.
I alerted our workshop and, looking at the photos, the workshop manager told me that it was probably the accessories drive belt (alternator and water pump) that had broken. It seems that this is the first time for all Thielert engines.
Comment from the declarant:
In the flight manual this failure is not considered, there is therefore no associated procedure.
The speed and “brutality” with which the alarms came one after the other can undoubtedly destabilize a pilot with little experience.
The “coolant overheating” procedure is intended for an engine which overheats when climbing (which has already happened on this type of engine) and which allows the temperature to return to normal.
The “low coolant level” (leak expected) procedure (which has already happened on this type of engine) involves diversion to the nearest field, possibly an IVV (emergency landing), but the engine temperature remains stable as long as it there is enough liquid.
In the case of a water pump failure, the engine immediately overheats and can “break” in the minutes that follow if it is not put to idle.
As stated above, the red low level coolant light also comes on. It was necessary to add 1.5 liters of liquid to compensate for the loss by boiling (capacity 5 liters). Engine idling time after breakdown less than 3 minutes.
I think two possibilities should be considered in protecting against this type of failure.
Training associated with an EMERGENCY procedure which allows the pilot to know that he will have to immediately make an emergency landing.
A modification of the cooling circuit by adding an electric water pump to be used as the fuel pump in the event of engine failure (switch) or automatically (pressure drop) with trigger indicator.
In the case of a water pump failure, the engine immediately overheats and can “break” in the minutes that follow if it is not put to idle.
If you must have one, driving the water pump on an aircraft engine with a rubber belt strikes me as a very bad design choice. The water pump is not an accessory on these engines.
Even while designing an engine with a power density requiring some level of liquid cooling, Rotax mitigated the associated safely issue on the 912 (in the 1980s) by liquid cooling only the heads and adding a design requirement that allows you to limp to an airport at low power with total liquid cooling system failure. The automotive derived four cylinder diesels don’t have this feature and it’s not a happy thing.
From my point of view, I’m surprised that belt failure never happened, it happens sometimes in cars… Once we had a failure in the club while renting an Ecoflyer, called a serious leakage in initial climb, but it was probably a belt issue. It was just not correctly reported because the plane renter went here very quickly to repair it.
Fortunately we don’t have ecoflyer anymore.
We have recently had a cooling problem on CD135 as well. In fact if greg_mp hadn’t mentioned the ecoflyer and some of the other details I would have thought it was ours.
But in our case there’s a bit more to the story which I can’t write about here because investigations are still going on. But one thing we do know is it’s going to be very expensive, perhaps a new engine.
The failure of the belt did happen in one of our Club 172‘s. The engine had to be replaced after this incident. I don‘t,know, if this got reported.
