Balfour Der told the three federal judges on the panel that Lieut. Darryl Watts of Calgary was put in an untenable position when he was placed in charge of the training range in February 2010.
Cpl. Josh Baker was killed and four other soldiers were injured when a C-19 Claymore anti-personnel mine misfired.
Der said Watts made it clear he was untrained on the C-19 and shouldn't be held responsible.
"Lieut. Watts was not under a specific or particular duty for the C-19 firing range. He was never asked to do it. He was never told to do it. The duty was given to (Warrant Officer Paul) Ravensdale," Der said.
"If it were somehow that Lieut. Watts had this overall safety duty, it would be a completely impossible task for a soldier," he added.
"How could we reasonably expect Lieut. Watts to be in control of all of these things at the same time? It's not a luxury. It's not even a possibility."
The lawyer suggested that Watts should be acquitted or at least granted a new trial. He argued that the military judge erred by not giving jury members the opportunity to acquit if they believed the accused was telling the truth.
Watts was found guilty in December 2012 of unlawfully causing bodily harm and negligent performance of military duty. He was demoted two ranks to lieutenant from major and given a severe reprimand.
He is appealing both his sentence and his conviction.
The prosecution has filed a cross-appeal and is seeking a harsher sentence.
Prosecutor Maj. Anthony Tamburro said it didn't matter that Watts wasn't trained on the C-19. He said Watts was in charge of the platoon and was responsible for his soldiers' safety.
"Simply having someone else take the hands-on training doesn't remove you from being in charge," said Tamburro, who noted that Watts was familiar with the safety manual on the C-19.
"He was there. He saw where the firing point was. He sees the people were not under cover and he does not intervene. In the military, people in the lower ranks expect those in the higher ranks will do things properly."
One appeal panel member questioned why Watts should be held responsible if he wasn't fully trained.
"He said he didn't know what to do. You're charging someone with what amounts to a fairly serious criminal offence," said Federal Court Justice Elizabeth Bennett.
She also questioned how Watts could anticipate possible injuries from firing the C-19.
"There's no ifs about it. It (the manual) makes it clear you need to be dug in and behind cover," said Tamburro.
"To say it is not foreseeable that someone could not see you could be hurt in the danger area, I would say that is untenable."
Baker, 24, died when the anti-personnel mine loaded with 700 steel balls peppered his platoon on the practice range. Four other soldiers were hurt when they were hit by the blast.
During arguments on sentencing, Der recommended Watts be reinstated as a major and receive a simple reprimand. The prosecution is requesting 18 months in jail. It also wants Watts dismissed with disgrace from the Canadian Forces and to be subject to a DNA order.
The appeal panel reserved its decision.
The prosecution argued during his trial that Watts, who was the platoon commander, didn't enforce safety standards and abdicated his duty as leader when he handed over responsibility for range safety to Ravensdale.
Watts argued that he had never been trained on the C-19 and as a result was not qualified to be in charge.
The day of the accident the range was divided into four training sections. The first two tests of the anti-personnel mine went off without a hitch. But during the next one, the ball bearings fired backwards, hitting Baker and the others.
Videos show several soldiers, including Watts, standing around and watching the test. They are not inside armoured vehicles or standing behind them for cover, as set out in military safety regulations.
Two other soldiers have also been convicted for their roles that day.
Christopher Lunney pleaded guilty Sept. 13, 2012, to negligent performance of duty for failing to ensure Watts was properly qualified on the C-19. He said he had assumed that to be the case because of Watts's rank. Lunney was demoted one rank to captain from major and received a severe reprimand.
Ravensdale, who was running the exercise that day, was found guilty last year of breach of duty causing death, breach of duty causing bodily harm, unlawfully causing bodily harm and negligent performance of military duty. He, too, was acquitted of manslaughter.
The now-retired soldier was given a six-month suspended sentence. He also received a fine and was demoted one rank to sergeant.
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