Expert Tech/know Your Lim­its


Electric Flight - - CONTENTS - By Gus Calderon

Un­der­stand­ing FAA, op­er­a­tional, and per­sonal lim­its is key to safe fly­ing

At 7:20 p.m. on Sept. 21, 2017, a DJI Phan­tom 4 had a midair col­li­sion with a U.S. Army Black Hawk he­li­copter fly­ing off the shore­line of Staten Is­land, New York. The col­li­sion dam­aged a main ro­tor blade and a win­dow on the up­per left-hand side of the he­li­copter, forc­ing the crew to make an emer­gency land­ing at Lin­den Air­port in New Jer­sey. The Army he­li­copter was op­er­ated by the 82nd Air­borne Divi­sion and was one of two Black Hawks as­signed to a se­cu­rity pa­trol dur­ing the United Na­tions Gen­eral Assembly meet­ing in New York City in ad­vance of the U.S. pres­i­dent’s ar­rival.

How It Hap­pened

The Na­tional Trans­porta­tion Safety Board (NTSB) launched an in­ves­ti­ga­tion into the crash, the first in­ci­dent of its type to have oc­curred in U.S. airspace. The Fed­eral Avi­a­tion Ad­min­is­tra­tion (FAA) con­firmed that it was as­sist­ing with the in­ves­ti­ga­tion but said that the U.S. Se­cret Ser­vice was the lead agency for me­dia in­quiries. The Fed­eral Bureau of In­ves­ti­ga­tion said that it was as­sist­ing the U.S. Army’s in­ves­ti­ga­tion. The New York Po­lice De­part­ment said it was also co­op­er­at­ing with the in­ves­ti­ga­tion, but it re­ferred ques­tions to the FAA and the U.S. mil­i­tary.

The NTSB Avi­a­tion In­ci­dent Fi­nal Re­port stated that one mo­tor and a por­tion of an arm of a Phan­tom 4 was found in the en­gine-oil cooler fan by Army main­te­nance per­son­nel. Us­ing the se­rial num­ber in­scribed on the mo­tor, fed­eral in­ves­ti­ga­tors were able to iden­tify, lo­cate, and in­ter­view the Phan­tom’s pi­lot, who has turned over flight data from the ground con­troller.

The NTSB Re­port stated the Phan­tom’s pi­lot in­ten­tion­ally flew the air­craft 2.5 miles away, well be­yond vis­ual line of sight. The pi­lot of the Phan­tom 4 was fly­ing for recre­ational pur­poses and did not hold an FAA Re­mote Pi­lot certificate or a manned air­craft pi­lot certificate. Ti­tle 14 Code of Fed­eral Reg­u­la­tions Part 101 man­dates hobby and recre­ational pilots main­tain vis­ual contact with their air­craft at all times and not in­ter­fere with the op­er­a­tion of manned air­craft.

While the airspace in the area of the flight is un­con­trolled (Class G), it was un­der­ly­ing a shelf of the Class B airspace and a No­tice to Air­men (NOTAM) is­sued by the FAA was in ef­fect at the time of the in­ci­dent. The NOTAM es­tab­lished a Tem­po­rary Flight Re­stric­tion (TFR) due to the United Na­tions Gen­eral Assembly meet­ing. The TFR re­stricted op­er­a­tions within the lat­eral lim­its of the New York Class B airspace. In ad­di­tion, an­other NOTAM was in ef­fect es­tab­lish­ing a VIP Pres­i­den­tial TFR over the crash site. Both TFRS in­cluded a pro­hi­bi­tion on model air­craft and un­manned air­craft sys­tems (UAS), and the Phan­tom pi­lot lit­er­ally flew from one TFR into an­other.

Op­er­a­tor Er­ror

Dur­ing the in­ter­view by fed­eral au­thor­i­ties, the Phan­tom pi­lot stated that he knew to stay away from air­ports, and that he re­lied on the DJI GO 4 app to “let him know if it was OK to fly.” He said he knew that the Phan­tom should be op­er­ated be­low 400 feet. When asked about the TFRS, he said he did not know about them and that the app did not give any warn­ings on the evening of the col­li­sion. The Phan­tom pi­lot said he was not aware of the sig­nif­i­cance of fly­ing be­yond line of sight and again stated that he re­lied on the app dis­play. He said he did not see or hear the pair of he­li­copters in­volved in the col­li­sion but ad­mit­ted know­ing that he­li­copters fre­quently flew in the area.

Al­though the pi­lot stated that he knew not to fly above 400 feet, his flight logs re­vealed that he had flown as high as 547 feet at a dis­tance of 1.8 miles ear­lier on the evening of the in­ci­dent. In ad­di­tion, even though the Phan­tom pi­lot said that he knew there were of­ten he­li­copters in the area, he still de­cided to fly be­yond vis­ual line of sight, which demon­strated his lack of un­der­stand­ing of the po­ten­tial col­li­sion hazard with other air­craft.

The DJI GO 4 app for the Phan­tom 4 in­cludes a fea­ture called “Geospa­tial En­vi­ron­ment On­line” (GEO), which is de­signed to help pilots avoid cer­tain types of airspace. GEO pro­vides pilots with real-time guid­ance about ar­eas where flight may be lim­ited by reg­u­la­tion, such as con­trolled airspaces and TFRS. Lo­ca­tions that raise se­cu­rity con­cerns, such as pris­ons, nu­clear power plants, and mil­i­tary bases, may also be iden­ti­fied. When avail­able and ac­ti­vated by the pi­lot, a mes­sage is dis­played on the con­trol de­vice iden­ti­fy­ing the type of airspace.

Ac­cord­ing to DJI, “The GEO sys­tem is ad­vi­sory only. Each user is re­spon­si­ble for check­ing of­fi­cial sources and de­ter­min­ing what laws or reg­u­la­tions might ap­ply to his or her flight.”

NTSB in­ves­ti­ga­tors also de­ter­mined that, at the time of the in­ci­dent, the TFR airspace-aware­ness func­tion­al­ity within GEO was not avail­able. DJI had tem­po­rar­ily dis­abled the fea­ture in Au­gust 2017 be­cause of tech­ni­cal prob­lems, and it was re­stored in Oc­to­ber 2017. DJI did not is­sue any no­tice to users that this ad­vi­sory func­tion had been dis­abled. The NTSB fur­ther em­pha­sized this fea­ture is in­tended for ad­vi­sory use only, and UAS pilots are re­spon­si­ble at all times to com­ply with FAA airspace re­stric­tions. Sole re­liance on ad­vi­sory func­tions of a non­cer­ti­fied app is not suf­fi­cient to en­sure that cor­rect airspace in­for­ma­tion is ob­tained. The best way to lo­cate airspace re­stric­tions is to use the FAA’S B4UFLY mo­bile app for recre­ational users or Airmap for Part 107 op­er­a­tors.

The NTSB de­ter­mined the prob­a­ble cause of this in­ci­dent to be “the fail­ure of the SUAS [small un­manned air­craft sys­tem] pi­lot to see and avoid the he­li­copter due to his in­ten­tional flight be­yond vis­ual line of sight. Con­tribut­ing to the in­ci­dent was the SUAS pi­lot’s in­com­plete knowl­edge of the reg­u­la­tions and safe op­er­at­ing prac­tices.”

FAA and Op­er­a­tional Lim­its

There are many lessons to be learned from this in­ci­dent, and ev­ery­one, es­pe­cially the Phan­tom 4 pi­lot, should be grate­ful there were no in­juries or fatal­i­ties. Clearly, there is still a lack of un­der­stand­ing of “safe op­er­at­ing prac­tices” among some mem­bers of the drone com­mu­nity, in par­tic­u­lar re­gard­ing flight lim­i­ta­tions.

There are ba­si­cally three types of lim­i­ta­tions in avi­a­tion. The first set of lim­its is im­posed by the air­craft man­u­fac­turer and may be called “op­er­at­ing lim­its” or “air­craft lim­its.” The sec­ond cat­e­gory are reg­u­la­tory lim­its im­posed by the FAA or other govern­ment agency, and the third cat­e­gory are per­sonal lim­its.

All manned air­craft have op­er­at­ing lim­i­ta­tions im­posed by the man­u­fac­turer. Full-size air­craft have lim­its that are care­fully tested and proven by FAA, and are cer­ti­fied for op­er­a­tion within those lim­its. Since drones are not cer­ti­fied by the FAA, it is sim­ply up to the man­u­fac­turer to do its own test­ing and de­ter­mine the op­er­at­ing lim­its.

Drone man­u­fac­tur­ers are not re­quired to pro­vide these lim­its to the user, so these lim­its are of­ten un­known. DJI has been mak­ing an ef­fort to pro­vide this in­for­ma­tion in its user man­u­als but the lim­its are not pre­sented in a stan­dard for­mat as they are for manned air­craft. A closer look at some of these lim­its in the user man­ual for the DJI Phan­tom 4 will help ex­plain the re­la­tion­ship among the three types of lim­its:

The max­i­mum al­ti­tude is 1,640 feet. It is widely known (hope­fully) that the reg­u­la­tory limit for fly­ing drones is only 400 feet. The Phan­tom 4 has two flight modes: P-mode and A-mode. The 400-foot-al­ti­tude limit is pre­set in the P-mode, and it is not pos­si­ble to ex­ceed that limit. If the A-mode is se­lected, it is pos­si­ble to fly the Phan­tom 4 up to 1,640 feet above the take­off point. The stan­dard traf­fic­pat­tern al­ti­tude for manned air­craft while in the vicin­ity of an air­port is 1,000 feet, so this would put the drone in an ex­tremely dan­ger­ous flight area.

The max­i­mum range is 4.3 miles. FAA reg­u­la­tions state the air­craft must be kept within vis­ual line of sight. This reg­u­la­tion is in­ter­est­ing be­cause the FAA does not give a spe­cific dis­tance for this limit. The ac­tual dis­tance will de­pend on the size of the drone, light­ing con­di­tions, and eye­sight of the pi­lot. In other words, this reg­u­la­tory limit is es­tab­lished by the pi­lot’s per­sonal lim­its. The pi­lot needs to de­ter­mine this limit dur­ing each flight, and the ac­tual dis­tance may vary de­pend­ing on the lo­ca­tion and con­di­tions. Since most drones now have teleme­try data dis­played on the pi­lot’s ground con­troller or smart de­vice, it is pos­si­ble to know the drone’s ex­act dis­tance at all times. Pilots can and should know the ac­tual dis­tance at which their drone be­comes dif­fi­cult to see and then re­duce that num­ber by 10 per­cent or more as a safety mar­gin.

The max­i­mum wind speed is 22mph. While the FAA does not have any spe­cific limit for flight in high winds, it does man­date that all air­craft are flown in a safe man­ner. In­ten­tion­ally op­er­at­ing in winds more than 22mph with a Phan­tom 4 could be con­sid­ered op­er­at­ing in a care­less and reck­less man­ner. Since the dawn of avi­a­tion, pilots have been con­cerned about high winds, and ex­pe­ri­enced pilots are al­ways aware of both cur­rent and fore­cast con­di­tions. The max­i­mum wind speed for each drone is a crit­i­cal limit be­cause, once it is ex­ceeded, the drone will not be able to main­tain po­si­tion, even in GPS mode.

Pilots should be aware that the wind speed is not al­ways con­stant, and strong gusts of wind are un­pre­dictable and may push the drone away and even out of sight. Wind speed usu­ally in­creases with al­ti­tude, and the ac­tual wind speed above sur­round­ing ground struc­tures may be sig­nif­i­cantly higher than ex­pected. When fly­ing on windy days, it is im­por­tant to be pre­pared to re­act with a mem­o­rized emer­gency pro­ce­dure. In most cases, it is best to cut the throt­tle im­me­di­ately and de­scend rapidly since wind speeds usu­ally de­crease the closer you get to the ground. Ma­neu­ver­ing to an area that is pro­tected from the wind (such as the down­wind side of a build­ing or struc­ture) will also help main­tain con­trol dur­ing the land­ing. Hav­ing a per­sonal limit for max­i­mum wind speed is im­por­tant, and in­ex­pe­ri­enced pilots should fly only in calm winds.

Per­sonal Lim­its

Novice drone pilots may find it dif­fi­cult to set per­sonal lim­its be­cause they just don’t have the ex­pe­ri­ence to make an in­formed de­ci­sion. Keep in mind that de­ter­min­ing your per­sonal lim­its is part of the learn­ing process. When pilots start to think about set­ting per­sonal min­i­mums, they usu­ally start with weather con­di­tions. Per­sonal lim­its are your lim­its, tai­lored to your ex­pe­ri­ence, strengths, and weak­nesses.

Per­sonal lim­its will also change based on your level of pro­fi­ciency. For ex­am­ple, a pi­lot who has been fly­ing in high winds dur­ing the day for many months will be­come more pro­fi­cient in these con­di­tions. Sim­i­larly, a pi­lot who has been fly­ing at night in calm winds for many months will be­come more pro­fi­cient op­er­at­ing in the dark. Clearly, the pi­lot who flew only dur­ing the day would not be pro­fi­cient at night fly­ing and vice versa.

The re­spon­si­bil­ity for de­ter­min­ing pro­fi­ciency is a judg­ment call by the pi­lot, and this is some­thing that comes with ex­pe­ri­ence. An in­di­vid­ual’s def­i­ni­tion of “pro­fi­cient” may vary ac­cord­ing to his or her skills, knowl­edge, and ex­pe­ri­ence. In the ab­sence of firm guid­ance, it’s up to pilots to de­ter­mine whether or not to go fly­ing and what con­di­tions are ac­cept­able to avoid a sit­u­a­tion that ex­ceeds their skill level or the drone’s lim­its. Per­sonal lim­its are de­ter­mined to help guide pilots through the de­ci­sion-mak­ing process.

Once your per­sonal lim­its have been de­ter­mined, some of them can be pro­grammed into the DJI GO 4 app. Max­i­mum flight al­ti­tude and ra­dius lim­its may be put in the app and changed at any time. If you are in­ex­pe­ri­enced, DJI also cre­ated the Be­gin­ners mode, which re­stricts flights to an al­ti­tude and height of 30 me­ters (100 feet). It is im­por­tant for pilots to iden­tify and un­der­stand their per­sonal lim­its to the same de­gree they con­cern them­selves with air­craft lim­its and reg­u­la­tory lim­its. Af­ter all, does any­one want fed­eral agents and in­ves­ti­ga­tors to knock on the front door?

Warn­ing screen dis­played on the B4UFLY app when drone is in con­trolled airspace.

Above: Mes­sage from the FAA dis­played when open­ing the B4UFLY app.

Be­low: Warn­ing from the FAA to all drone users dis­played when open­ing the B4UFLY app.

Map dis­play page on the B4UFLY app show­ing a drone within con­trolled airspace.

Begin­ner Mode se­lected by the user on the DJI Go4 app. Both al­ti­tude and flight lim­its are set to 30 me­ters 100 feet by de­fault.

Flight al­ti­tude and dis­tance lim­its man­u­ally se­lected by the user on the DJI Go4 app.

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