### National Tran s port ation Safety Board Wash ing ton, DC 20594 Office of th e Chairman April 8 , 2015

The Honorabl e Michae l P. Huerta Administrator Fede ral Aviation Administration Washington, DC 20591 Dear Adm in istrator Hu e rta: Thank you for your Febru ary 5, 2015 , letter to the National Transportation Safety Board regarding Safety Recomm e ndation s A-0 9 -55 through -58 , and A-09-60. We issued th ese recommendations to the Fe deral Aviat i o n Adm inistrat ion on Jul y 17 , 2009 , as a result of o ur in vesti gat i on of the Sept e mber 19 , 2008 , runway overrun by a B o mbardier Learjet 60 , operated by G l obal Exec Av iation , wh il e departing Co lumbi a Metropolitan Airport , Columbia , So u th Ca rolina. A-09-55 R

eq uir e L earjet to change the design of the Lea1jet 60 thrust le ve r s yste m in future -manu factured airplanes so that the r everse lever positions in th e cockpit match the positions of th e thrust re verser mechanism s at th e e ngines when the thrust reversers stow
. A

- 09-56 Once des ign changes are developed pe r Saf e ty Recommendation A-09-55, r equire Learjet 60 ope r ators to retrofit exist in g airp l anes so that the reverse lever positions in th e cockpit match the positions o f th e thrust rev erser mechanism s at the e ngin es w

he n the thrust re verse rs stow
. A

- 09

- 57

l0 1 50<l il 3 Require Lear j et to develop and in stall improved aura l or v i sual cues on future manufactured Learjet 60 airplanes that wou ld all ow pi lots to recognize an inadve rtent thrust reverser stowage in a timely manner.2
A-09-58 Once improved aural or visual cues are developed per Safety Recommendation A-09-57, require Learjet 60 operators to install those cues on existing Learjet 60 airp lan es. Your current l etter discusses the June 13 , 2013, issuance of airworthiness directive (AD) 2013-13-09, which requires installing n ew rigid hydraulic tube assemblies to the main landin g gear (MLG) struts, modifications to the MLG squat switch system , improved wheel well electrical w irin g protection , and system shielding; and the April 1, 20 10 , issuance of AD 20 I 0-1 I -II to reduce the r isk of tire fai lure on Learjet 60 airplanes , includin g revisions to the crew procedures for an aborted takeoff and in advertent stow of thrust reverser after a crew-commanded deployment. We have previously said that these developments are commendable and needed improvements, but they are not relevant to these recommendations. You previously to ld us that you had determined that an unsafe condition existed when full reverse thrust i s com manded but f ull for.vard thrust is obtained after a failure, and that , as a result, Learjet was developing a change to the thrust reverser system on the Learjet 60 to mitigate this unsafe conditio n. You said that you p l anned to certify Learjet's revised design. We replied that these were positive steps towards satisfying Safety Recommendations A-09-55 and -56. ln your previous letter, you also told us that you believed that the changes being made to the thrust reverser actuator controls also addressed Safety Recommendations A-09-57 and -58
. We did not agree, and we sa id that the need remained for the development and installation of aura l or visual cues when the thrust reversers had not deployed as commanded. In your current letter, this s itu ation i s now reversed. Learjet i s developing an au r al warning as recommended in Safety Recommendation A-09-57, but wo rk on the des i gn change to make the positions of the thrust reverser l evers match the positions of the thru st reversers is on hold pending development of the proposed aural warn in g. You state that you believe the aural warn in g may be a more cost-effectiv e and readily implemented alternative to the actions specified in Safety Recommendations A-09-55 and

- 56. We continue to believe that a ll four r eco mmended actions are necessary and that none of the actions for any one or pair of these recommendations i s an acceptable alternative for the others. Becaus e you have placed the planned activity on hold, Safety Recommendations A-09-55 and -56 are classified " Open

- Unacceptab l e R espo nse" pending completion of the recommended actions. Because Learjet i s now designing a system to provide an aural warning , Safety Recommendations A-09-57 and -58 are class i fied "Open

- Acceptable Response" pending completion of this system, your rev iew and certification of the system, and your requiring that it be incorporated into newly manufactured and in-ser v ice Learjet 60 airplanes
. A-09-60 Eval uate the design of the thrust reverser controls and indications in Raytheon Hawker I 000 business jets for potential thrust reverser failure modes3 

### that are sim il ar to those identified 111 

### Learjet 60 airplanes and implement necessary changes
. We note that you continue to eva luate the effectiveness of the design change that Textron Aviation

-Beechcraft (formerly Hawker Beechcraft Company) deve loped to ensure that the engine remains at idle follow i ng a failure cau sing an uncomm anded stow of the thrust rev erser. We further note (1) 

### that Textron Aviation is integrating Beech craft and Cessna in to a s ingle company, (2) that the company is in the process of comp l eting certification tasks associated with the des ign change, and (3) that you asked Textron Aviation-Beechcraft to provide a schedu l e update for their next tasks. P en ding completion of the recommended action, Safety Recommendation A-09-60 remains classified "Open-Acceptable Response. " Please submit updates electronically at correspondence @. ntsb.gov regarding your actions to address these recommendations
. Please do not submit both an e l ectronic copy and a hard copy of the same response .

cc: Ms. Barbara McCann , Director Office of Safety, Energy, and

E nvironment Office of the Under Sec retary for Policy S in cerely ,

### &·**ristophcr** A. Hart

· '/. C hnirmnn

..... • A..'\?:tJH'rl ;rY crt ·C:tc.r. :c**il.itW~t ~·** **dl'** N' 1-lon:**~" .tr**  F uo·...,

## National Transportation S afety Board Washington , D.C

. 20594

T he Ho no rable J. Randolph Babbitt A

dmini s tra t or Fe d e ra l A viatio n Administration Washin g to n , D
. C
. 20591 

### Safety Recommendation

Date: July 17 , 2009 In reply refer to: A-09-55 through -60

On S e ptemb e r 19 , 2008 ; about 2353 eastern daylight time , a Bombardier Learj et 60 ( Learjet 60) , N999LJ , operated by Global Exec Aviation , overran runway ll while d e partin g Co lumbi a Me tropolitan Airport, Columbia , South Carolina. ' The pilot, copilot, and two o f the fo ur p asse nge rs w ere killed ; the two other passengers were seriously injured
. The aircra ft w as d es tr oye d by pos tcrash fir e . Visual meteorological conditions prevailed , and an instrum e nt fligh t r u l

es fli gh t plan was fil ed for the 14 Cod e of Fe de ral Reg ulations (C FR) Part 135 non sc he dule d d o me stic passe ng er fligh t to Van N uy s , California. Acco rding to witness interview s and th e cockpit voice recorder (CVR) transcri pt , th e b eg inni ng o f th e tak eoff roll appeared normal. H ow ever , s parks were observed as the airpl ane tr a vel ed al o ng the runway . The airplane then con tinued bey ond the runway and throu g h th e approximately 1 , 000-foot runway safety area and , beyond that , struck airport lighting , navigati on f a cili ties, a perimet e r fe nce, and c o ncrete marker posts. T he airplane then cr osse d a roa d way an d ca me to res t when it s truck an e mbankmen t across th e ro ad fr om the airport. P

os tacc id ent examinati o n of markin gs and tire debris indic a t e d th a t th e ri g ht o utbo ard tir e fai l e d fi rs t bec au se o f und e rinflati o n, f o ll o w e d by failures o f the oth e r tires. 2 Examin a ti o n of t he e ngin es r evea l e d e vidence con s istent with hi g h thrust in both en g ines and indic a t ed th at t he th ru st reve r se rs we r e s towed w hen the airplane hit th e e mbankment. The Nati o na l Tr a n sp o rta ti o n Saf e t

y Bo a rd ' s (NTSB ) inv es tigati o n of thi s acc id e nt i s o ngo in g . H ovveve r, on th e ba si s of pre liminar y findin g s , the NT SB i s co nce rne d abo ut s af ety

1 Mo r e info rm at i o n abo u t th is acc id e nt , DC A0 8 MA098, i s ava il ab le on t h e Nati ona l Tran spo rt ation Safety Boa rd 's webs i te at < http: // www .nts b. g o v/n ts b / q uery.asp > . 2 Duri ng t he investi gati on, t he NTS B fo und ev id e nce t ha t th e acc i de nt airpl a ne's t ires w ere u nde rin flated. Review of t ire f rag me n ts r evea le d t hat th e re was ex t e n s ive he at d a m age within th e t ire co n struct i on; excess i ve we i ght (ove r flexu r e) of th e rubb e r c reat ed th e h ea t. No ev id e nce of exces s i v e bra ke hea tin g was fo und. T he t ires are be in g separate l y add r esse d.

806JA2
issues involving in advertent s t owage 3 of the thrust reversers . In Mar ch 20 0 9, Learjet publ i shed a Federal Av ia tion Ad mini st r atio n ( FAA)-approved te mp orary flight manual (TFM) c hang e in procedu r es , wh ich described improved methods fo r quickly recognizing and ha n d li ng sit uatio ns when i nadverte nt stowage occurs . Howeve r, the NTSB is conce rn ed that Learjet 60 p i lots are not s uff i c i ently trained to rec og ni ze that a**t~ lilurc**  could occ ur dur ing takeoff as well 

### as l an din g phase s of flight a nd could sub se qu en tl y result in the loss of system logic control requirem ents for maintaining deplo ye d thru s t r eve rs ers dur ing a r e j ected takeoff
. The design of the Learjet 60 th ru st r everse r sys t e m (and potent i ally similarly de s ig ned systems for Raytheon Hawker 1000 bus i ness jets) i s a lso of concern to the N T S B. Informat ion su pportin g six recommendations to address these safety i ssues is d isc u ssed below
. De s ig n ofLear j et 60 T hr ust Lever System Review of the CVR reve a l e d that t he first indic at ion of tire damage occurr ed after t he a irp la n e had passed V 1 4 and that fl i g ht crew actions we r e co nsistent w ith a dec i s i o n to reject the takeoff. 5 The Learjet 60 rej e cted takeoff procedure calls for the pil ot to r e du ce thrust to idl e, deplo y the rever se lev e rs , and then increase thrust whil e in re ver s e . A so und spectrum a n alys is of t he CVR indic a t e d that the e n g in e power was reduced and then increase d to about 80 pe r cen t o f maximum power, consistent w ith the pilot following the r ejecte d tak eoff procedure. On most transport-category airplanes, includin g the Le arje t 60, to de pl oy the thr ust r eversers, the p il ot first mov es the engine pow er levers to id l e then pu ll s the r everse le ve rs upward. T h e levers' up ward defle cti o ns determ in e h ow much r eve rse thr ust is c r eated
. In Learjet 60 a irpl anes, there is no mechanical or cab le - actuated con nection betwee n the reve rse l eve rs and the e ng in e thrust reverse rs . When th e r eve rse leve rs are ra ised, an elect ri ca l sig n al comman ds the thrust reve rs ers to go to a reverse thru st position. T h e syste m must m eet ce rta in requirements before the thrust r eve rse rs w ill move to a r everse thru st p os iti o n ; for example, th e a ir /g r ou nd sensor squat switches, located on the m a in landing ge ar, mu st indi cate th at the a irplan e is on the ground (by d etecting weight on whee l s)
. T he e l ect ronic engin e contr()ls ha ve no ability to auto m at i cally r e turn the reverse l evers · to the idl e posit i o ns and do not reduce the thrust if the sys tem control log i c r equ irements for keeping the thru st reve rsers deployed ar e no longer being met. In ad d i ti o n , the thrust reversers are des i g ned to fai l to the s towed position to allow forwa rd thru st a nd prevent red u cti on of p il ot cont rol in flight
. The wi r ing fo r the accident airplane's right squat switch was ro uted a lon g the ri g ht main landin g gear str ut between the right tires. G la ss from the ad jace nt landing li ght and ev idence of a broken h ydra uli c hose were found amo ng the first tire f r agme nts, and data on t he CVR ind i cated

3 A lt hough t his sit uation is ref erred to as "inadvertent" stowage, it is n ot th e result of any c r ew-commanded act ion
. 4 V 1 is the takeoff decision spee d or crit i cal engine fa i lure speed
. Follow ing a fai lure of the critica l e ng in e, V 1 is the m inimum s pee d in the takeoff at which th e pilot can contin ue t akeoff a nd achieve the req ui red height above the takeoff surface wi thin the takeoff distance . V 1 is also the maximum speed in the takeoff at wh i ch th e p il ot mus t take t he first actio n (for examp le , apply brakes , reduce thru s t , deploy speed brakes) to stop the a ir p l

ane with in the acce ler ate-stop distance. 5 The tires began to fai l just as the first office r said, "V 1 ." In addition, during the invest i gation, t he NTSB learned about an FAA t est pi l ot o f a Learjet 55 who rejected a t a keoff after multipl e t ires fa il ed at V 1 ; the pi l o t reported that he ma d e t he dec i s i on because he was afra id that the engines would in ges t numerous large t ire pieces that we r e being thrown past the cockp it windows
.3
that a s quat switch ci r cuit went to the "a ir " mode during the accident sequence. 6 These findings are strong indications that the squat switch wiring was probably damaged when the tires failed
. Thus, with the loss of the on-ground s ign al , th e system wou ld have moved both thrust r eversers to the stowed position (the position in which the accident airplane's thrust reversers were found). Acco rd ingly, the engines would have provid ed forward thrust commensurate with the angle of the thrust lever position commanded by the pilots , even though the reverse levers \Vere in the reverse posiliun
. The only way to reduce forwa rd thrust und er these abnormal circumstances is to move the reverse levers to the stowed position. However, moving the rev erse l eve rs to the stowed position wo ul d be counterintuitive to a pilot who was try ing to reject a takeoff by applying maximum reverse thrust. Initiall y, flight crewmembers trying to slow the airplane would likely think that they a r e receiving the reverse thrust that they commanded until they realize that the airplan e is not slowing. Therefore, the NTSB recommends that the FAA require Learjet to c hange the design of the Learjet 60 thrust lev er system in future-manufactured airplanes so that the reverse le ve r positions in th e cockp it ma tc h the positions of the thrust rev erser mechanisms at the engines when the thrust reversers stow. Once design changes are developed per Safety Recomme ndation A-09

- 55, the NTSB recommends that the FAA require Learjet 60 operators to retrofit existing airplanes so that the reverse l ever positions in the cockpit match the positions of the thrust reverser mechanisms at the engines when the thrust reversers stow
. Lc arjct 60 Thrust Reverser Indications Norma ll y, six lights 7 -three for each engine

- will illuminate on the fo rward instrument panel t o indicate the status of the thrust reverser s (see figure)
. E ach bottom light (TR ARM) is gree n and indicates that prerequisites for reverse thrust exis t, suc h as the availability of hydraulic pressure to dep loy the engine thrust reversers . Two of the conditions that trigger the TR ARM ljghts and that wou ld be apparent to the pilots were that (I) the sq uat switches sense that the a;rc raft i s in ground mode, and (2) the engine power levers are in the idle positions. Th e T R ARM lights denote that the reverse levers can be moved up ward if the pilot elects
. Becaus e these lights are norma lly on whe n the eng in es are at the idl e position on the ground and go out whenever the engine power le vers are moved to and from idle, the pilot ca n become conditioned to these lights go in g on and off during normal taxi
. When the r everse l evers are raised to the DEPLOY position, hydrauli c pressure unlocks the engine thrust reverser doors, and, subsequently, t\vo amber li ghts (TR UNLOCK) wi ll illuminate · to indicate that both thrust r eve rse r doors are unlocked. When the amber TR UNLOCK lights illuminate , the green TR ARM li ghts extingu i sh. After the engine thrust r e verser doors are fully deployed, two wh ite li ghts (TR DE PLOY) illuminate, and the amber TR UNLOCK lights extingu i sh.

6 A nose gea r steering disconnect t one was heard on t he CVR, which was an indi cation that th e squat switch w ent to a ir mode. The alert was advisory, under th e condit i ons in this accident; no pilot action was needed. 7 On Learjet 60 airp lan es, indicator lights for the left thrust reverser are located on the left s id e of the instrume nt pa nel ( in f ront of the pilot), and lights for the right thrust reverser are on the ri gh t side (in front of the cop ilot )
.4

Thrust 

### reverser indicator lights

F i gure. Diagram of a Learjet 60's lights on the main annunciator panel. Source: F l i gh t Safety I n ter nat ional**Lea~et** 60 P ilo t Tra i ning Manual, Vo l ume 1 , Rev i s i on 1. If, during a rejected**takeoff~** th e r e were an in advertent thrust re verse r stowage due to l oss of the requirements for mainta inin g reverse thrust, the follow i ng indications would occur:
• T he white TR DEPLOY li g ht(s) wo uld ext in gu is h,

o The amber TR UNL OC K light(s) would illuminate momentarily, and

o T he green TR .ARJ.\t lli g ht(s) would b li nk mo m ent aril y . 8 The o nl y indic at ion available to th e p il ots that the cock pit reve rse levers and eng in e th r ust rev e rse rs were not in agree m e nt wou l d be th e p il ots' co mpr ehe n s i o n that neith e r of the TR D E PLOY lights was illuminated whil e the reve rse l eve rs were in the positio ns norma lly assoc i ated with reverse thrust. T h e NTSB conc lud es that, during a rejected takeoff, whi ch r equires quick and concentrated pi l ot actions , it ma y be diffi c ult for a pilot to recog ni ze the sig ni fic an ce o fthe absence of reverse thrust indicat o r lights . In the March 2009 TFM revi sion, Learjet ex panded its rejected takeoff pro ced ure by a d v isi ng that, if none of th e engin e annunciator lights for both rev e rse rs i s iI I um inat ed, th e revers e rs have stowed. A dditi onally, a note was added to c larify the normal se quenc ing of the ann un c iat or l ights whe n thrust reve rsers are dep l oye d
. T h e NTS B is concerned that Lea rj et 60 ai rplan es s till do not provide suffic ient cu es for pilots to be able to quic k l y recognize an in advertent thrust reverser sto wage (and r esu ltant forward thr ust) and then make tim ely decis i ons and act o n the m. In add ition to h av ing a system in w hich the reverse leve r position matches th e e ng in e thru st r eve rs er position , similar, more mo dern airplanes have a v i sual indi catio n that in fo r ms t h e fl ight crew . (especially the nonflying pilot whose hand most likely i s n ot on t he l ever) that the reve rsers have inadv ertent l y s towe d. T herefore , the NTSB recommends that the FAA requ ir e Learj et to deve lop and in stall impr oved aural or visua l cues on future-ma nufact ur ed Lear j et 60 airp lanes that wo uld allow pilots to recognize an inadv erte nt thrust reverser stowage

s The MASTER CAU TION light may illuminate momentar il y if the MASTE R CAUTION is not inhi bited d urin g takeo ff ; inh ib i t in g the MASTER CAUTION light is a no rmal par t oft he Learjet 60 t akeoff procedure
.

### 5
in a timely manner. Once improved aural or vis ual cues are deve loped per Safety Recom mendation A-09-57, the NTSB recommends that the FAA require Learjet 60 operators to in stall th ose cues on ex isti ng Learjet 60 airplanes. Inadv e rtent Thrust Reve rser Stowage Procedure During initial ce rtification of Lemjet 60 airplan es, Learjet developed an ab n o rm a l proced u re in the event o f an in advertent thrust reverser stowage. Fo ll owing a January 1 4, 2001, Learjet 60 acc id e nt, 9 Lear j et amended the procedure; it i s now an e merge ncy proc ed ur e titled
" In adve rtent Stow of Thrust Reverser After a Crew-Commanded Deployment." The proced ure, located in the Learjet 60 Crew Checkli st and in the Quick Refer ence Handbook (QRH), stat es in part: INADVERTENT STOW OF THRUST R EVERSE R AFTER A CREWCOMMANDE D DEPLOYME NT 1. Maintain control with rudd e 1; aileron, nose wheel steering & brakes 

### 2
. Both Thrust Reve rser Levers
........................ STOW{JOJ Steps 1 and 2 li s t e d above are conta in ed in a hatched box in the QRH indicating that the steps are to be performed by memory. The M arc h 2009 TFM re vision for Le arjet 60 airplanes added a warning to this pro cedure and to the rejecte d takeoff procedure ; the warning advises Learjet 60 o perato rs that a damaged s q u at sw itc h could potentially cause in adverte nt thru s t reve rse r stowage. The warning a lso d

. esc ri bes e ng ine power lever mov e m e nts and light indication s on the cockpit pan e l and o n the e ng in e ind i cat ion syste m pan e l that r esu l t from the damag ed squat switch and stat es that, if a d

_ a maged squat sw itch (or its fai lures ) cau ses in advertent thrust reverser stowage r es ul tin g 111 fo rw ard thrust , then the thrust revers e r l eve rs mu st be stowed immed i ately. Afte r this accident , investigators in terviewed num e rou s pilot s and in s tructor s and found that th e Inadvertent Stow of Thru st Reverser procedure w a s includ ed durin g initi al tra ini ng on the ai rpl a n e . However, pilots and instructors said that th e inadv e rt ent s t owage scen ari o was us uall y ta ug ht durin g landin g phases rather than during takeoff pha ses. Another example of damaged sq u at sw itch w iri ng causing inadv e rte nt thrust r eve rse r stowage o n takeoff occurred in J un e 1998. Acco rdin g to a vo lun tary pi lot r epo rt s ubmitted to the National Aeronau ti cs a nd

9 On J anuary 1 4, 200 1 , a Learjet 60 regis t e r ed to a nd o pe rated by A rk -A ir, In c ., co llid ed with deer short l y after to uc hd ow n at Tro y M unicipa l A irp ort, Troy, A l abama, cont i nue d down the runway •vith tires smok in g, veered o ff t he ri gh t side of t he runway , and imp acted a ditch b efore bursting into flam es. According to the pil ots, th e eng in e th r u st re versers fa il e d to oper ate when engaged. A sou nd spect r um s tudy co n ducted by the NTSB indi cated th at e ngine th rust in creased from 82.4 t o 90.4 percent during the l an din g rollout and that the thrus t r eversers expe ri enced a n ina dvertent stowage. Exami nati on of the land in g gear fo und all three gea r s collapsed and deer fur l odged i n the squa t sw it ch o n t he left main landing gear. Mo re in fo rm ati on abo ut this incident, ATLO l F A021, is ava ila ble on t he NT SB's websi t e at < http: //www .nt sb
. gov/ ntsb/ queJy . asp> . As a res ul t of thi s event, L earjet changed the squ at sw itch circuitry to preven t in adver ten t t hrust rever ser stowage after an a irp lane had taken off and flown, but t he desi g n change di d n o t prevent an inad verte nt s t owage from occ urrin g durin g a re jecte d takeoff. 10 M ovin g bot h th rus t r everser levers to s t ow woul d reduce comman d ed t hrust to idl e .

### 6 Space Ad ministration's aviation safety reporting system, in the June 1998 event, the engine thrust r everser system was rendered inoperative due to damage to the squat switch syste m. In this event, a Learjet 60 experienced a failure of both right main tires during takeoff from Wash in gton Dulles International Airpo r t, Chantilly, Virginia. The tire failure resulted in the disintegration of the right main brake assembly, which severed the hydraulic lines and electric connections to the antiskid system and the squat switch system. The NTSB concludes that**~raining** for in adve rtent stowage of thrust reversers during only landing phases is insufficient to prepare pilot s for this situation during rejected takeoff, when the airplane has greater acceleration energy. T herefore, t he NTSB recommends that the FAA require that all Learjet 60 pilots receive training, for takeo ff as well as landing phases of flight, on recognizing an inadvertent thrust reverser stowage, in c luding the possibility that the stowage can occur when the requirements for deploying thru st r eversers are not fully met, suc h as when the air/g r ound sensor squat sw itc h circuits are damaged. Pilots must be aware that this can result in forward thrust even when the r everse levers ar

e in the r everse thrust position. Similarly Designed Raytheon Hawker 1000 E ng i ne Installation T h e NTSB is aware that the engine installation for Raytheon Hawker 1000 bu s iness jet s shares numerous s imilariti es with the engine installation for Lea1j et 60 airplanes. Both airp lane models use Pratt & Whitney PW305 engines and have similarities in the e l ectro nic engine controls, thrust revers er systems, and indications. Because of the sim ilariti es, the NTSB recommends that the FAA evaluate the design of the thrust reverser controls and indi cat i ons in Raytheon Hawker 1000 business jets for potential thrust reverser failure modes that are simi lar to thos e identified in Lemjet 60 airplanes and implement necessary change s . The r efore, the Nationa l Transportation Safety Board recommends th at th e Federa l Av ia t i on Adm ini stratio n:

Require Lea1jet to change the design of the Lemjet 60 thrust lever system in future -manufa ctured airplanes so that the reverse lever po s ition s in the cockpit match the positions of the thrust reverser mechanisms at the e ngines when th e thrust reversers stow
. (A-09-55) Once design changes are developed per Safety Recommendation A-09

- 55, require Lem j et 60 operators to retrofit existing airplanes so that the reverse lever positions in the cockpit match the positions of the thrust reverser mechanisms at the engines w

h

en the thrust reversers stow. (A-09-56) Req uire Learjet to develop and install improved aural or visual cues o n futu re manufactured Lear jet 60 ai rpl anes that would allow pilots to recognize an inadvertent thrust reverser stowage in a timely manner. (A-09

- 57) Once improved aural or visua l cues are developed per Safety Recommendation A-0 9 -57 , require Lea1j et 60 operators to install those cues on ex isting Learjet 60 airplanes. (A-09

- 58)

### 7
Req uir e rhat all Lea 1jet 60 pilots receive training , for tak eoff as we ll as land in g phases of flight, on r ecogni z in g an inad ve rtent thru s t reverser stowage, includin g the poss ibili ty that the stowage can occur when the require ment s for deplo y in g thru st reversers ar e not full y m et , s uch as \ N

h

e n the air /gro und sensor squat sw itch c ir c uit s ar e damaged
. ( A

- 09

- 59) Ev aluate the design of the thrus t reverser control s and indications in Rayth eo n Hawker I 000 business jets for potential thrust revers e r failure modes that are si milar to tho se id ent ifi ed in Lea1j et 60 a irpl anes and implement neces s ar y changes
. (A-09-6 0) I n re s ponse to the recommendations in this letter, please refer to Safety Recommendations A-09-55 through -60. If you wo uld li ke to su bmit your response e lectronicall y r ather th a n in hard copy, you may send it to the following e-mail address : co rres po nd e nce @ nts b. Q:OV. If your res p onse includes attachments that excee d 5 megaby tes, p l

ease e - mai I us asking for in structions on h ov.r to use our Tumbl eweed secure mailbox p

r oced ur e s. To avo id confusion, pl e as e u se o nl y one method of submission (that is , do not submit bo th an elec tronic copy and a hard copy of th e same response letter). Acting Cha irman 

### ROS ENKER and Me mb ers 

### HERSMAN , HIGGINS, and SUMWALT co ncurr ed with th ese recommendation s . [Original Signed} By: Mark V. Rosenker Actin g Chairman