UNITED KINGDOM AERONAUTICAL INFORMATION CIRCULAR

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1 NATS Ltd UK Aeronutil Informtion Servie Hethrow House Bth Rod Hounslow, Middlesex TW5 9AT URL: Phone: Phone: Phone: UNITED KINGDOM AERONAUTICAL INFORMATION CIRCULAR (Editoril) (Distriution - Tngent Diret) (Content - Flight Opertions Poliy/Engineering) AIC: P 077/ SEP-2009 Sfety Cnels AIC 145/1997 (Pink 161) INDUCTION SYSTEM ICING ON PISTON ENGINES AS FITTED TO AEROPLANES, HELICOPTERS AND AIRSHIPS. 1 Introdution 1.1 Piston engine indution system iing, ommonly, ut not ompletely urtely, referred to s rurettor iing my our even on wrm dys, prtiulrly if they re humid. IT CAN BE SO SEVERE THAT, UNLESS CORRECT ACTION IS TAKEN, THE ENGINE MAY STOP. Indution system iing is more likely t low power settings suh s those used during desent, holding, on the pproh to lnding or during uto-rottion on heliopter. 1.2 Sttistis ontinue to show n verge of 10 ourrenes, inluding seven idents, per yer whih were proly used y engine indution iing. After fored lnding or ident the ie my well hve disppered efore n opportunity ours to exmine the engine, so tht the use nnot positively e identified. 1.3 Some irrft nd engine omintions re more prone to iing thn others nd this should e orne in mind when flying nother irrft type. 2 Indution System Iing 2.1 There re three min types of indution system iing: Crurettor Iing: The most ommon type of indution system iing is rurettor iing whih is used y omintion of the sudden temperture drop due to fuel vporistion nd the redution in pressure t the rurettor venturi. The temperture redution my e s muh s C nd results in moisture in the indution ir forming ie. The ie grdully uilds up, onstriting the venturi, nd y upsetting the fuel/ir rtio uses progressive derese in engine power. Engines whih hve onventionl flot-type rurettor re more prone to this type of iing thn re those whih hve pressure jet rurettor, ie: the Stromerg type of rurettor. Engines with fuel injetion system re not, of ourse, sujet to rurettor iing; 1.

2 Fuel Iing: Fuel iing is the result of wter, held in suspension in the fuel, preipitting nd freezing in the indution piping, espeilly in the elows formed y ends; Intke or Impt Ie: Ie whih uilds up on ir intkes, filters nd rurettor het or lternte ir vlves et, is known s intke or impt ie (for onsisteny the term impt ie is used throughout this Cirulr). Impt ie n umulte in snow, sleet or suzerotemperture loud or in rin when the temperture of the rin or the irrft is elow 0 C, this type of iing ffets fuel injetion systems s well s rurettor systems. 2.2 Testing hs shown tht, euse of the greter voltility nd possile greter wter ontent, rurettor nd fuel iing is more likely to our with MOGAS thn with AVGAS. 2.3 Redued power settings re more onduive to iing in the throttle re euse there is greter temperture drop t the rurettor venturi nd the prtilly losed utterfly n more esily e restrited y the ie uild-up. 3 Atmospheri Conditions 3.1 Crurettor iing is not onfined to old wether nd will our in wrm wether if the humidity is high enough, espeilly when the throttle utterfly is only prtilly open s it is t low power settings. Flight tests hve produed serious iing t desent-power with the mient (not surfe) temperture ove 30 C, even with reltive humidity s low s 30%. At ruise power, iing n our t 20 C with reltive humidity of 60% or more. Ie retion is less on old, dry winter dys thn on wrm, humid summer dys euse the wter vpour ontent of the ir is lower. Thus, where high reltive humidity nd mient tempertures of etween -10 C nd +25 C re ommon, s is the se in the UK nd Europe, pilots must e onstntly lert to the possiility of iing nd should tke the neessry steps to prevent it. If the pproprite preventive tion hs not een tken in time it is vitl to e le to reognise the symptoms (see prgrph 4.2) so tht orretive tion n e tken efore n irretrievle sitution develops. Should the engine stop due to iing it my not re-strt or, even if it does, the dely my result in ritil sitution. 3.2 Crurettor or fuel iing my our even in ler ir nd these re, therefore, the most insidious of the vrious types of iing euse of the lk of visul lues.the risk of ll forms of indution system iing is higher in loud thn in ler ir ut euse of the visul lues the pilot is less likely to e tken unwres. 3.3 Speifi wrnings of indution system iing re not inluded in stndrd wether forests for vition. Pilots must use their knowledge nd experiene to estimte the likelihood of its ourrene from the wether informtion ville.when informtion on the dewpoint is not ville, pilots in the UK nd Europe should lwys ssume high reltive humidity, prtiulrly when: d e f The surfe nd low-level visiility is poor, espeilly in the erly morning nd lter evening nd prtiulrly when ner lrge re of wter; the ground is wet (even with dew) nd the wind is light; just elow the loud se or etween loud nks or lyers; in preipittion, espeilly if it is persistent; in loud or fog - these onsist of wter droplets nd therefore the reltive humidity should e ssumed to e 100%; or in ler ir where loud or fog hs just dispersed. 2.

3 3.4 The hrt elow shows the wide rnge of mient onditions onduive to the formtion of indution system iing for typil light irrft piston engine. Prtiulr note should e tken of the muh greter risk of serious iing with desent power. The loser the temperture nd dew-point redings, the greter the reltive humidity. CARBURETTOR ICING IN AIR FREE OF CLOUD, FOG OR PRECIPITATION (risk nd rte of iing will e greter when operting in loud, fog nd preipittion) Serious iing ny power Moderte iing ruise power Serious iing desent power Serious iing desent power Worldwide pproximte upper limits of dew-point NW Europe Light iing ruise or desent power +10 Dew-point C Temperture C 3.5 Impt iing ours when flying through snow or sleet, or in loud in whih super-ooled wter droplets re present. It n our, ut is less frequent, when flying through super-ooled rin or on n irrft whih hs surfe temperture elow 0 C when through rin whih is ove freezing temperture. The mient temperture t whih impt ie my e expeted to uild up most rpidly is out -4 C in onditions in whih visile ie is forming on other prts of the irrft. 4 Prevention, Reognition nd Remedil Prties 4.1 Prevention Whilst the following provides generl guide to ssist pilots to void indution system iing, the Pilot s Operting Hndook or Flight Mnul must e onsulted for speifi proedures pplile to prtiulr irfrme nd engine omintion. The proedures re likely to vry etween different models of the sme irrft type. In most omintions, rurettor iing is prevented y heting the intke ir in n exhust het exhnger efore it rehes the rurettor (design requirements typilly demnd temperture rise of 50 C t 75% power). This is usully hieved y use of mnully operted rurettor het ontrol, mrked HOT or COLD, whih, in the HOT position, y-psses the norml intke filter nd derives the indution ir from heted soure. The HOT position should e seleted in time to prevent the formtion of ie, euse if the seletion is delyed the use of hot ir might e too lte to melt the ie efore the engine stops. It should e noted tht engines with rurettor het seleted to HOT will not produe full power due to the inlet hrge heting effet reduing the intke hrge density, produing redution in volumetri effiieny. This loss in power should not e onfused with the effets of rurettor iing; severl engine/irfrme omintions het prts of the intke or rurettor eletrilly. Use of these eletril systems is unlikely to use more thn miniml redution in power, so eletril heting should e pplied in ordne with the mnufturer s instrutions whenever the onset of rurettor iing is likely; engines with fuel injetion normlly hve n lternte ir intke, mrked ON or OFF, loted within the engine owling nd operted y vlve downstrem of the norml intke. Although the ir does not pss through het exhnger it derives some het from the engine. Some engine instlltions hve utomti lternte ir seletion tivted y pressure-sensitive vlves. 3.

4 d e other thn on tke-off, the HOT AIR position should e seleted periodilly when iing onditions re suspeted or when flying in onditions of high humidity with the outside ir temperture within the high proility rnges indited on the hrt t prgrph 3.4. Unless expressly permitted the ontinuous use of the HOT AIR position should e voided, espeilly during hovering flight in heliopter. It should e seleted intermittently for long enough to pre-empt the loss of engine power (due to iing); this time period will vry dependent on the previling onditions. s onsequene of the inresed suseptiility to rurettor iing t redued power settings, for oth ir nd eletril systems, the HOT position should e seleted prior to desent, pproh nd lnding. 4.2 Reognition Should no preventtive tion hve een tken, or ws tken too lte, or ws insuffiient, the onset of indution iing my e reognised in the following wys: With fixed-pith propeller, slight drop in RPM is the first sign whih my indite the onset of iing in the indution system. If not retified there will e loss of irspeed nd/or height. The loss of RPM my e grdul with no ssoited rough running. The usul retion is to open the throttle slightly to restore the RPM nd this tion msks the erly symptoms. As the iing inreses there will e rough running, virtion nd further RPM redution; loss of irspeed or height will result nd ultimtely THE ENGINE MAY STOP. Thus the min detetion instrument is the RPM guge used in onjuntion with the Air Speed Inditor. where onstnt-speed propeller is fitted, nd in heliopter, the loss of power would hve to e lrge efore the RPM redued, hene the onset of indution system iing ould e even more insidious. However, the effet of iing will e shown y drop in mnifold pressure nd then y redution of irspeed or height. The primry detetion instrument is, therefore, the mnifold pressure guge. Engine rough running my provide n dditionl indition. n exhust gs temperture inditor will show derese in Exhust Gs Temperture (EGT) with the onset of iing ut engine rough running proly would hve een deteted lredy. 4.3 Remedil Ation When the presene of indution system iing is suspeted the HOT or lternte ir ON position must e seleted immeditely. The reommended prtie with most engines is to use full het whenever rurettor het is pplied. The ontrol should e seleted fully to the HOT position. Prtil heting n indue indution system iing euse it my melt ie prtiles whih would otherwise pss into the engine without using troule, ut not prevent the resultnt mixture from freezing s it psses through the indution system. Alterntively prtil het my rise the temperture of the ir into the ritil rnge. with some engine instlltions the use of prtil rurettor het my e onsidered, prtiulrly where n intke temperture guge is fitted. An intermedite position etween HOT nd COLD should only e used if n intke temperture guge is fitted nd pproprite guidne is given in the Flight Mnul. Note: It should e rememered tht the seletion of the HOT position fter ie hs lredy formed my t first pper to mke the sitution worse euse of the redution in power due to the use of hot ir nd to n inrese in rough running s the ie melts nd psses through the engine. If this hppens the tempttion to return to the COLD position must e resisted in order tht the hot ir my hve time to ler the ie. This my tke 15 seonds or more nd my seem very long time in diffiult irumstnes. 5 Mintenne nd Hndling Proedures of HOT AIR Systems 5.1 Mintenne The indution heting system nd ontrols should periodilly e heked for proper ondition nd opertion. Prtiulr ttention should e pid to the ondition of sels whih my hve deteriorted nd re llowing the hot ir to eome mixed with old ir nd thus reduing the effetiveness of the system. 5.2 Strt-Up The engine should e strted up with the rurettor het ontrol in the COLD position or with the lternte ir seletor in the OFF position, s pplile. 4.

5 5.3 Ground Txiing The use of hot or lternte ir while txiing is not normlly reommended euse in most engine instlltions this ir is un-filtered, hene there is risk of dust nd foreign mtter eing ingested. However, if engine run down ours this my indite tht indution system iing is present nd the use of hot ir will e the only wy of preventing further prolems. 5.4 Pre Tke-off Engine Run Up The RPM or mnifold pressure setting should e noted efore seleting HOT AIR. The pilot should hek tht there is the pproprite derese in RPM nd/or mnifold pressure when the HOT position is seleted (out RPM nd 3-5 mnifold), nd tht the inditions re regined ut not inresed when the COLD position is re-seleted fter 15 to 20 seonds. If RPM or mnifold pressure hve inresed from the previous figure, ie ws lmost ertinly present. The hek should e repeted s required until no rise is pprent, nd the pilot should e redy to rry out further heks efore tke-off. 5.5 Immeditely Prior to Tke-off Indution iing n our when txiing t low power or when the engine is idling. If the wether onditions pper to e onduive to the formtion of indution iing then the HOT position should e seleted efore tke-off for suffiiently long to remove ny umultion whih my hve ourred. If the irrft is kept t the holding point in onditions of high humidity it my e neessry to run up the engine to the tke-off power setting more thn one to ler ny ie whih my hve formed. The tke-off must not e ommened if the pilot hs ny suspiion tht rurettor iing is present. 5.6 Tke-off When the throttle is fully open for tke-off the pilot should hek tht the mnifold pressure nd/or RPM re orret for the irrft type. The stti RPM with fixed-pith propeller will e less thn the mximum RPM pproved for the engine ut the relevnt vlue should e known for eh irrft. Crurettor het must not e seleted to HOT nor lternte het to ON during tke-off unless speifilly uthorised in the Flight Mnul or Pilot's Operting Hndook. 5.7 Clim (inluding hovering flight in heliopter) The pilot should e lert for symptoms of indution iing, espeilly when visile moisture is present or when the dew-point nd mient tempertures re lose, inditing high reltive humidity. 5.8 Cruise The pilot should monitor the RPM, mnifold pressure, indution or rurettor ir temperture guge, or EGT for slow deline whih would indite the onset of indution system iing. The pilot should periodilly selet the HOT AIR position for long enough, s in prgrph 5.4 ove, to hek for the presene of indution iing. The pilot should mintin the HOT seletion nd rememer tht it my tke 15 seonds or more to ler the ie nd the engine my run roughly s the ie melts. If the iing is so severe tht the engine stops, the HOT seletion should e mintined s the residul het my still e suffiient to melt the ie nd enle power to e restored. If impt iing is enountered HOT or lternte ir ON should e seleted in se the seletor vlve eomes immovle due to pked ie. Clouds should e voided s muh s possile. 5.9 Desent nd Auto-rottion Flight in Heliopter As redued throttle openings re muh more onduive to the formtion of rurettor iing, the HOT position should e seleted efore the throttle is losed for the desent or n uto-rottion, i.e. efore the exhust temperture strts to fll. The HOT seletion should e mintined during prolonged periods of flight t redued throttle settings, e.g. during long desents t low power, nd engine power should e inresed with HOT AIR still seleted to ruise settings t intervls of pproximtely 500 ft so s to inrese exhust tempertures in order to melt ny ie whih hs formed Downwind The pilot should either selet HOT AIR during the pre-lnding heks or inlude hek of the rurettor het in the pre-lnding heks nd oserve the redution nd susequent inrese in mnifold pressure nd/or RPM Bse Leg nd Finls Unless stted to the ontrry in the Pilot's Operting Hndook or Flight Mnul the HOT position should e seleted on se leg efore the power is redued for the pproh. On some engine instlltions, to ensure etter engine response nd to permit go-round to e initited without dely, it is reommended tht the rurettor het should e seleted to COLD t out 200/300 ft on finls Go-Around or Touh nd Go If the rurettor het hs not een seleted to COLD on finls this should e done onurrently with the pplition of go-round power, or s shortly therefter s is possile After Lnding The pilot should ensure tht the rurettor het hs een seleted to COLD or the lternte ir to OFF efore txiing. 5.

6 6 Min Points 6.1 It is etter to prevent ie uilding up thn to ttempt to melt it. 6.2 Indution system iing forms insidiously. 6.3 Iing n our in wrm nd humid onditions, nd is possiility t ny time of the yer in the UK nd Northern Europe. 6.4 The pilot should e wre of the possiility of the formtion of indution system iing nd e prepred to tke pproprite preventive mesures in time. 6.5 Crurettor iing is more likely to our t low power settings. 6.6 When flying in onditions onduive to the formtion of rurettor iing the HOT position should e seleted periodilly nd ertinly t the first indition of redution in RPM, mnifold pressure, irspeed or height. 6.7 Some irrft/engine omintions re more suseptile thn others. 6.8 Use of MOGAS inreses the possiility of rurettor iing. 6.9 Unless the Flight Mnul or Pilot's Operting Hndook uthorises different proedure the HOT/ALTERNATE ir ontrol should e seleted fully ON or OFF If ie hs een llowed to form it will tke some time to melt nd the engine my run roughly while this is hppening - PERSIST! 6.